calrad
TRANSCRIPT
CALRAD
Student Study Guide
1997 Version
CALRAD
Calrad has been written by a consortium of Universities and has been funded by the University
Funding Council’s Teaching and Learning Technology Programme (TLTP).
The consortium is made up of six member universities:
University of Dundee, Department of Medical Physics (Lead Site).
Project Director Dr. R. A. Lerski
Project Co-ordination Mrs. Jennifer Wilson
and Educational Design
Software Development Mr. Stewart Morrison
Multimedia Development Mr. John Dickson
University of Aberdeen Dr. B. Heaton
University of Edinburgh Mr. Williams
University of Glasgow Dr. M. Davison
University of Liverpool Dr. P Cole
University of Newcastle Dr. D. J. Rawlings
We have received funding from the Teaching and Learning Technology Program (TLTP). The
Teaching and Learning Technology Program is jointly funded by the four UK higher education
funding bodies, HEFCW, SHEFC and DENI.
Please Note: This document is only the study guide and not the CALRAD computer program.
Contents
CHAPTER 1 INTRODUCTION
CHAPTER 2 TEXT FROM THE CALRAD BOOKS
Book 1: Basic Physics of Radiation
Book 2: Radiation Quantities and Doses
Book 3: Biological Effects and Risks
Book 4: Aims of Radiation Protection
Book 5: Safe Use of X-ray
Book 6: Safe Use of Radionuclides
Book 7: Radiation and Pregnancy
Book 8: Rules and Regulations
GLOSSARY OF TERMS
Chapter 1: Introduction
This CALRAD Student Study Guide and the CALRAD computer program cover the knowledge that
is required for those working with Ionizing Radiation in accordance with recent EC Regulations and
an Act of Parliament, The Ionizing Radiation (protection of Persons Undergoing Medical
Examination or Treatment) Regulations 1988.
The regulations recommend that all practicing Medical staff should be fully trained in a Core of
Knowledge in the theory and practice of the use of Ionizing Radiation in medicine.
The aim of the CALRAD program is to teach this required Core Knowledge.
This student Study Guide has been designed to complement the CALRAD program. It contains much
of the textual of the material from the CALRAD program which may be useful for future reference.
The Glossary of Terms which is available at the end of this Study Guide should be of particular use
for future reference.
The last Chapter in the Students Study Guide has been rewritten to reflect the Law and Rules and
Regulations in force in the UAE.
As you progress through the books, you will cover information which is relevant to certain cases on
the Case Menu. You will be directed to attempt certain cases at an appropriate stage.
After Completion of: You will be directed to:
Book 4 Case 1: “Diagnostic Imaging”
Book 5 Case 2: “Fluoroscopy”
Book 6 Case 3: “Searching in Vein!!”
Book 7 Case 4: “Any Requests?”
As you work through CALRAD remember to use:
• Lists of aims on the last page of each book
• Summaries on the last page of each book
• Self-Assessment Questions
• Performance Meter in the cases
Your answers to the Self-Assessment are not part of any formal assessment and your answers are not
recorded. The questions are intended to give you an idea of your progress and to highlight areas of
weakness in your knowledge and understanding. Low scores would suggest that you should revise
parts of the package or revise appropriate sections in this Study Guide.
Chapter 2 : Text from the CALRAD Books
Book 1: Basic Physics of Radiation
Patients receive radiation doses in medicine from four sources: Nuclear Medicine, Diagnostic
Radiology, Dental Radiology and Radiotherapy.
This book will address the following questions:
• What is radiation and what forms of radiation are used in medicine?
• What are the properties of the different forms of radiation?
• Why does radiation need to be handled carefully?
Structure of the Atom
In order to understand how radiation is produced and how it interacts with human tissue, it is
necessary to look at the structure of the atom. All radiation originates at the level of the atom.
Atoms are made up of a nucleus, which contains protons and neutrons, and electrons, which spin in
orbitals around the nucleus. Atoms are electrically neutral as they have equal numbers of positively
charged protons and negatively charged electrons. As all atoms of carbon contain 6 protons, the
Atomic Number of carbon is 6. If an atom of carbon also has 6 neutrons then the Mass Number is 12.
All atoms of a particular element contain the same number of protons in the nucleus. For example, all
atoms of carbon contain 6 protons. However, not all atoms of carbon contain the same number of
neutrons. Atoms of the same element which contain different numbers of neutrons are called
“isotopes” of that element.
Nuclides The stability of the nucleus can depend on the numbers of protons and neutrons that it contains.
However, it is possible for two nuclei which contain identical numbers of neutrons and protons to be
in different energy states.
The term “nuclide” will be used from now as this term defines a nucleus by the number of protons
and the mass number, as well as the energy state of the nucleus if relevant. Here is an example of two
different nuclides of the element technetium which have an identical composition and chemical
behavior but exist in different energy states and their radioactive decay is quite different:
Technetium 99m and Technetium 99 (m stands for metastable)
Technetium 99m is in a metastable state where excess energy is temporarily retained in the nucleus
after its formation. When the nucleus returns to its lowest energy state, the nuclide becomes
technetium 99.
The stability of nucleus depends on the number of protons and electrons. There are at least 1000
different nuclides, both natural and man-made. Only about 200 of these are stable, the rest are
unstable. Almost all elements up to atomic number 83 (bismuth) have one or more stable nuclide(s)
and all elements have one or more unstable nuclide(s) (either natural or man-made). These unstable
nuclides are called “radionuclides”.
Unstable nuclides or radionuclides undergo a process called radioactive decay, in which the unstable
nuclide transforms itself to a different nuclide by emitting radiation. If this process does not result in
a stable nucleus being produced then further radioactive decay may take place.
Processes by which an atom may decay include beta particle emission, alpha particle emission,
emission of gamma radiation, isomeric transition, internal conversation, electron capture and
spontaneous fission.
In beta decay, one of the neutrons becomes a proton plus an electron (beta radiation):
This means that the Atomic Number increases by 1 while the Mass Number stays the same. For example, the equation for molybdenum 99 undergoing beta decay would be:
A beta particle may also be a positive electron produced in the transformation of a proton to a
neutron, In this case it is more usually known as a positron,
Molybdenum also emits gamma radiation at the same time as it is emitting beta radiation. The
gamma radiation is a release of energy and does not affect the Mass Number and Atomic Numbers in
the equation.
In alpha decay the nucleus loses a helium nucleus consisting of two protons and two neutrons.
The activity of a sample of a radionuclide is the number of decays per second and is measured in a
unit called the Becquerel (Bq). The activity of a sample of radionuclide decreases with time and if it
is measured it is found that:
“The time that is required for the activity of a sample of a radionuclide to decrease to half its
value is a constant, which is called the half-life of that radionuclide”.
Here is a graph illustrating the decay in the activity of a technetium-99m Sample which has a half-
life 6 hours:
Different radionuclides have different half-lives, varying from fractions of a second to many billions
of years, although those in medicine tend to have half-lives of a few hours or days.
Radiation
The most common types of radiation which are emitted during the radioactive decay of different
radionuclides are alpha, beta and gamma radiation.
Beta and gamma radiation are used in medicine.
Radionuclides which emit alpha are not used in medicine.
Other forms of radiation that may be used in medicine include protons, neutrons and heavy ions but
they tend to be just for research purposes.
X-rays are another form of radiation that is very commonly used in medicine. X-rays are not obtained
from radionuclides but are produced by an X-ray machine. In an x-ray machine, a voltage of many
thousands of volts is applied between two electrodes, in the x-ray tube. The negative electrode
(cathode) is heated to emit electrons which are accelerated to the positive electrode (anode) with a
tungsten target.
The electrons are stopped abruptly when they bombard the atoms of tungsten. About 1% of the
energy that is produced is emitted as X-rays. If the current is increased then more X-rays will be
produced.
Properties of Radiation
Alpha and beta radiation are both charged particles of radiation. Gamma radiation and X-rays are
electromagnetic radiation, which means that they have no mass and they have no electric charge.
They are an invisible, highly energetic form of energy wave rather like visible light.
The Spectrum of Electromagnetic Radiation:
Gamma rays and X-rays are at the light energy end of the spectrum. Gamma radiation and X-rays can have identical energy and the only difference is that gamma
radiation originates in the nucleus while X-rays originate in the electron shells.
Penetration of Radiation
Alpha and beta radiation are charged particle radiations and they have a definite range in matter. For
example, beta can travel up 2mm through human tissue:
It is not possible to predict the range of a particular beam of electromagnetic radiation (gamma
radiation and X-rays), although it is possible to say that a certain fraction of the radiation will be
absorbed depending on the thickness of the absorber.
To illustrate:
Energy of Radiation
Radiation of a particular type can be of varying energy i.e. beta rays do not all have the same energy
and X-rays do not all have the same energy. It is possible to vary the ranges of energy of the X-rays
that are being produced in an X-ray machine by changing the voltage settings on the machine. If the
voltage (kV) that is being applied across the X-ray tube between the cathode and the anode is
increased then the X-rays that are being produced will be of a higher average energy. The operator
can also increase the current (mA) in order to produce more X-rays.
Gamma rays are emitted at one or more discrete energies which are characteristic of the radionuclide.
For example, the radionuclides cobalt 60 and technetium 99m both emit gamma radiation. However,
cobalt 60 emits the gamma rays at energies 1173 keV and 1332 keV, almost ten times higher than
does technetium 99m (140 keV).
Extent of Penetration
The energy with the particular radiation is given off from the radionuclide or the X-ray machine will
make a difference to the extent of penetration. At higher energies, x and gamma radiation become
more penetrating. The extent of the penetration of radiation also depends upon the density and
composition of the matter. For example, radiation will penetrate fat, soft tissue and bone to different
extents. The basic principle of how an X-ray image is formed is that when X-rays are passed through
the body, some will be absorbed, some will be scattered and some will pass straight through. The X-
rays will penetrate the bones and soft tissue to different extents. The Unabsorbed X-rays go straight
through the body and blacken a photographic plate placed behind the patient. The plate remains
unblackened where the X-rays have been absorbed en-route by bones or other dense tissues. This
resulting white-on-black X-ray image (radiograph) can give diagnostic information.
X-ray images can be used for conventional radiography, for real time imaging (fluoroscopy) and for
axial (slice) images in Computed Tomography (CT) scanners etc.
Ionisation
Matter is made up of many atoms. When the different forms of radiation pass through matter they
can cause ionization by removing electrons from the atoms. This results in the formation of
electricity charged ions in the matter.
Alpha, beta gamma radiation and X-rays cause ionization to occur, therefore, these types of radiation
are called “Ionization Radiation”
The various types of radiation cause ionization in different ways:
Alpha: Alpha particles can cause a great deal of damage by ionization over a short distance because
they have a double positive charge which will attract electrons form atoms and they have a great
mass, which means that they move slowly through tissue relative to beta and gamma radiation.
Although alpha particles will not penetrate the dead (outer) layer of skin, if alpha emitters are
breathed into the lungs and come in contact with the living cells of the lung surface they can cause
lung cancer. Miners working in Uranium mines which have high levels of Radon gas, an emitter of
alpha radiation, have been found to have high levels of lung cancer.
Reference: Stedley, C.A; Samet, J.M.,A Review of Ecological Studies of Lung Cancer and Indoor Radon. Health
Phys. 65:234-251;1993.
Beta: Beta particles have a single negative or positive charge, which means that when they pass close
to atoms or molecules they can attract or repel electrons from thousands of atoms along their path,
leaving them ionized. Each ionization contributes to the slowing down of the particle. The path of
ionization from a beta particle could look like this:
If skin is contaminated with beta particles, skin burns may appear. “Beta burns” were seen in most of
those who died as a result of the Chernobyl accident.
Reference: Summer D., Wheldon T., Watson W., Radiation Risks, Tarragon Press, Glasgow 1994
Gamma: Gamma rays and X-rays do not carry electric charge and do not cause ionization directly
when interact with matter. Instead, they collide with atomic electrons, giving some or all of their
energy to the electron, which then causes ionization in the same way as a beta particle. The following
diagram illustrates how gamma rays interact with human tissue:
The following descriptions describe the four types of interactions which are illustrated in this
diagram, starting from the top of the diagram:
Elastic Scattering: A gamma ray bounces of an atom without losing energy.
Compton: The gamma ray interacts with an atom causing it to be ionized
when an electron is ejected. The gamma ray loses energy in the process but
goes on to cause further ionizations. The electron that has been ejected
behaves like a beta particle and goes on to cause ionization.
Photoelectric Effect: A gamma ray collides with an atom and all its energy is transferred to one
electron which is ejected from the atom leaving it ionized. This electron is
identical to a beta ray and goes on to cause ionization.
No Interaction: some gamma rays pass straight through the human tissue and do not cause
any ionization.
Damage It is possible for damage to occur when energy form radiation is transferred to matter such as human
tissue in the form of ionization. If the damage is not repaired then it is possible for permanent
damage to occur. Damage mechanisms are considered in greater detail in “Book 3: Biological Effects
and Risks”.
As the different types of radiation travel different distances through matter the damage that they
cause is spread out over different distances:
High LET Radiation:
Alpha radiation is called High LET (Linear Energy Transfer) Radiation because it causes a large
number of ions to be produced over a very short distance (up to 0.1mm in human tissue).
The distance between ionizing events is very short, much less than the dimensions of a tissue cell.
This means that they cause more biological damage for the same energy absorption compared with
low LET radiations.
Alpha emitting nuclides are not used in medicine because:
a) They are very difficult to detect
b) They are extremely hazardous if inhaled or ingested.
Low LET Radiation:
Beta radiation is called Low LET (Linear Energy Transfer) radiation because it produces relatively
sparse ionization. This is because beta particles travel mush faster that alpha particles and therefore
penetrate further matter.
Gamma and X-rays are also called Low (LET) radiation because the damage that they cause is spread
out over a large distance. They interact with the medium to generate secondary electrons, which are
the same as beta radiation, and it is these electrons which cause damage by ionization.
Because the damage that is caused by Low LET radiation is spread out, it often gives the body more
chance to repair the damage that has been done. This is in contrast to the alpha radiation (high LET
Radiation) where the damage is more localized.
Note: In radiotherapy, the ionizing property of the radiation is used to deliberately destroy abnormal
cells or tissues.
Scatter
There will also be a degree of scatter as the gamma radiation and X-rays pass through matter. This is
known as the Compton Effect:
The rays change direction during collisions with atoms in the matter. They can degrade X-ray image
and these scattered rays are also the major source of radiation for staff working in an X-ray room.
Protection of Persons
To protect staff and patients against the effects of radiation, it is important to consider these factors:
• Distance – All electromagnetic radiations obey the inverse square law, which means that:
• Shielding – The damage that is caused to human tissue by ionization during medical procedures
can be minimized using shielding. Lead shielding will REDUCE the number of gamma and
X-rays passing through and therefore lead is an effective shield against radiation. Both staff
and patients can be protected by the use of shielding against radiation. Both staff and patients
can be protected by the use of shielding. When working with X-rays you will find that staff
wear leaded aprons and work behind a lead glass window if at all possible. Patients can be
protected by shielding areas of the body which are not being X-rayed.
• Time – The greater time that you are exposed to a radiation source, the greater the radiation
dose you will receive. So when working with sources which emit gamma rays, you should
keep the sources in lead shielding for as long as possible
Book 2: Radiation Quantities and Doses
In subsequent books information will be given on the effects of radiation on patients. This book
introduces the units used to measure:
• The quantities of radiation involved
• The doses received by patients.
Activity
As already mentioned in Book 1, the activity of a radionuclide sample is measured in Becquerel’s
(Bq). One Becquerel corresponds to one decay per second.
A single becquerel is a very small amount of radioactivity so in practice activity is measured in
megabecquerels (MBq), or other multiples of a becquerel such as kilobecquerels (kBq). Please refer
to the Glossary for an explanation of prefixes in common use.
Absorbed Dose
It is necessary to link the effects of radiation with the amount of radiation received. One of the
simplest quantities to use is Absorbed Dose, which is the energy absorbed per unit mass. This is
measured in grays (Gy); 1 gray is defined as being equal to 1 joule of energy deposited in 1 kg of
tissue. In practice, since 1 gray is a very large dose as far as radiation protection is concerned, it is
more usual to measure absorbed dose in milligrays (mGy) or centigrays (cGy).
Equivalent Dose
Radiation damage does not depend only on Absorbed Dose, it also depends upon the type of
radiation. Equivalent dose is a quantity which is more closely related to biological effect.
This is calculated as:-
The radiation weighting factor takes into account the amount of tissue damage done by a particular
radiation, which depends upon its LET. The types of radiation generally used in medicine (beta
particles, gamma rays & X-rays) have a radiation weighting factor of 1 and so the equivalent dose is
numerically equal to the absorbed dose. However, this may not be true for other types of radiation.
See the Glossary for examples of radiation weighting factors greater than one.
The unit equivalent dose is the Sievert (Sv). 1 Sievert is a very large dose of radiation and so it is
usual to use submultiples millisieverts (mSv) and micro Sieverts (μSv).
1 millisievert (mSv) is roughly.
• 50 times the average radiation dose from a single film chest x-ray, or,
• the dose received from cosmic radiation in 50 return flights to the South of Spain !!, or,
• LESS THAN HALF the average annual dose from natural background radiation in UK
Reference: At-A-Glance Series, “Radiation Doses – Maps and Magnitude”, 2
nd
Edition, NRPB, 1994 and “Medical
Radiation”, NRPB, 1994
Effective Dose
On exposure to radiation, there is a varying dose to each tissue:
There is also a different amount of effect depending upon the sensitivity of the tissue. Not all tissues
are equally affected by radiation. To assess the overall effect on an individual, it is necessary to use
weighing factors to account for the radio sensitivities of the tissues irradiated. Each organ contributes
to the effective dose for the whole body and the contribution for one organ is calculated as:-
Refer to the glossary of Terms for information about Tissue Weighting Factors
The purpose of calculating the effective dose is to find the theoretical dose that would have the same
effect if applied uniformly to the entire body i.e. to carry the same risk.
The effective dose for the whole body is calculated as:-
As with equivalent dose, effective dose is measured in sieverts – in practice millisieverts (mSv) and
microsieverts (μSv)
This concept of effective dose to the whole body is an important one in radiation protection and
references to it will be made in Books 3, 4, 5 & 6 for the procedures covered in those books. In the
following books, the term effective dose will be referred to simply as dose unless we specify
otherwise.
Risk Factors
It is possible to calculate the risk of developing effects from an exposure to a certain quantity of
radiation.
This can be expressed as a percent per sievert.
You will come across this unit used to express the estimation of risk in Book 3.
Collective Dose (manSv)
Collective Dose is the total dose received by a population and is calculated by multiplying the
following:
“the average effective dose received” X “the number of people exposed to a
given source of radiation”.
The unit is the man Sievert (manSv).
If 10,000 people each receive, on average, 10 mSv (i.e. 10 x 10 -3
Sv) then the Collective Dose will
be:
10,000 “men” x 10 x 10-3
Sv = 100 manSv
Book 3: Biological Effects and Risks
This book will consider the following questions:
• What are the mechanisms for radiation damage?
• Which effects are deterministic and how do they relate to radiation dose?
• What is meant by stochastic effects and how do they relate to radiation dose?
• How are the risks assessed?
As has been in Book 1, when ionizing radiation passes through matter it interacts with the atoms and
loses energy, producing charged particles. This takes place almost instantaneously. The energy loss is
a random process along the track of the charged particle so that some molecules will be damaged and
others will not. Where the affected molecules are in living cells this may result either directly or
indirectly in cellular mutations.
Ionization within important macromolecules, such as the deoxyribonucleic acid or DNA of the cell
nucleus, can cause damage by direct action. Damage to DNA may be in the form of single or double
strand breaks, chemical alteration of the bases or chromosomal aberrations. Repair processes come
into play following the damage and for single strand breaks the repair may be completely error free,
as illustrated in this diagram:
However, double strand breaks are less likely to be repaired and this can lead to death of the cell or
failure to reproduce.
High LET radiation, such as alpha particles, is most likely to cause damage to cells by this direct
mechanism.
As well as causing direct damage to the DNA is a cell, it is possible for ionizing radiation to cause
damage indirectly. Ionizing of cellular water leads to the production of hydrogen and hydroxyl free
radicals. The hydroxyl free radical in particular is extremely reactive and can diffuse rapidly through
a cell causing chain reactions in nearby DNA resulting in similar damage to that from direct action.
Since 70 to 90% of the body is water this mechanism is more likely to occur that direct damage for
low LET radiation such X-rays, gamma rays and beta particles. Oxygen can also form a free radical
giving rise to enhanced DNA damage in oxygen rich cells. Conversely oxygen deficient cells
(hypoxic) are relatively resistant to radiation.
Sensitivity of Tissues
For actively dividing tissues, such as the bone marrow, germinal cells of the ovary or testis or the
epithelium of the intestine, the cell killing effect becomes apparent only a few hours or days after
exposure to radiation. For more slowly dividing tissues cell death may not occur until months or
years after exposure.
Somatic and Genetic Effects
Where biological effects are produced in the person receiving a radiation dose they are said to be
somatic effects – from the Greek ‘somaticos’, which means ‘of the body’.
Somatic effects may be deterministic or stochastic. The differences between these two types of
effects will be discussed in this book.
Where the biological effects are produced in the offspring of a person receiving a radiation dose they
are to be genetic effects.
Consideration should be given to the possibility that a radiation dose to a pregnant woman can give a
dose to the embryo or fetus. Irradiation “in utero” can lead to a number of effects that are not
possible in adult tissues. The effects can also depend upon the particular stage of organogenesis at the
same time of exposure. These effects will be considered in more detail in Book 7: Radiation and
Pregnancy.
Deterministic Effects
Deterministic effects have a dose threshold below which the effect does not occur and above
which, the effect is more or less certain to appear. When the severity of a deterministic effect is
plotted against dose, it can be seen that the severity increases non-linearly above the dose
threshold
However, it is IMPORTANT to note that the thresholds for deterministic effects are WELL ABOVE
the doses which occur in diagnostic radiology. But they may be exceeded in radiotherapy or in
serious radiation incidents.
Deterministic effects include erythema, nausea, depilation and cataracts. Each effect has a separate
dose threshold above which the effect is more or less certain to appear:
Deterministic effects can be considered rather like getting sunburn. If you are sunbathing in Spain for
3 hours with no suntan lotion you can expect to get a certain degree of sunburn.
Stochastic Effects
With the relatively low doses of radiation received by patients during diagnostic imaging procedures,
it is stochastic effects which are of particular concern.
Stochastic effects are where damage to the DNA does not lead to cell killing but may, nevertheless,
lead to other serious biological effects, for example:
• Initiation of the development of a cancer.
• Hereditary disorders in later generations.
The single cell mutations which have large scale consequences occur randomly.
The probability of a stochastic effect is proportional to the dose at low doses and dose rates. (There is
no dose threshold.)
All doses additive and no recovery is envisaged so that it is the total dose received over a person’s
lifetime that is important.
The severity of a stochastic effect is independent of the dose.
To explain this, consider that although the risk of cancer is less at lower doses, it is still possible for a
cancer to be induced, and the effects of this can be identical to a cancer which has been induced at a
higher dose.
Hence, the severity of the effect is independent of the dose.
Genetic Effects
If the damage caused by radiation is to the germ cells (the ovaries or the testes), this damage (in the
form of mutations and chromosomal aberrations) may be transmitted and be manifested as hereditary
disorders in the descendants of the individual who has been exposed. Although such effects have not
been identified in man, studies on animals and plants suggest that such effects will occur.
The consequences may range from minor effects to gross malformations or in extreme cases to
premature death. This type of stochastic effect is called a genetic effect.
Radiation Risk Defined
When discussing radiation risk we usually refer to the probability or the likelihood of exposure to
radiation leading to a harmful stochastic effect, such as cancer fatality or severe hereditary harm.
However, in some cases consideration of risk may include the nature and severity of the harmful
consequences, and even whether the risk is imposed or voluntary. As an alternative, some people find
it more useful to consider life expectancy than risk to a person.
Data Source for Radiation Risks
Information on cancer risks following radiation exposure to low LET radiation comes from many
sources, including:
• The study of more than 90,000 survivors of the atomic bombing in Japan in 1945,
• Follow-up of 14,000 patients who received medical treatment with X-rays for ankylosing
spondylitis.
• The Marshall Islander exposed to radiation in atomic bomb tests.
Supporting data from other radiotherapy treatments are also used to assess risk to specific organs.
Estimated Cancer Risk in the UK
The following risk factors show the varying sensitivities of organs and tissues to fatal cancers after
exposure to radiation for the UK Population:
The estimates were made on the basis of data from exposure at high doses and dose-rates,
extrapolated to the low doses and dose-rates encountered in diagnostic radiology. Furthermore it was
necessary to extrapolate from the period of observation to the full lifetime using models to estimate
the excess risk of cancer from a radiation dose. Extrapolation inevitable leads to some uncertainty in
the risk. These risk factors are applicable both to members of the general public and to patients. For a
working population, the risk reduced slightly relative to the risk to the general population, because of
the more limited age range.
Reference: NRPB Volume 4, No. 4 (1993) “Estimate of Late Radiation Risks of the UK
Population”
The most recent TOTAL risk estimate for fatal cancer in the UK Population (all ages and sexes) as
result of being exposed to doses and dose rates encountered in diagnostic radiology is given by the
National Radiological Protection Board (NRPB) as 5.9 % per Sv.
Risk of Cancer to Children
Radiation risks in childhood are greater than is adults. Two reasons for this are:
• For delayed effects, such as cancer induction, there is a longer time period for the risk to be
expressed.
• Children have a higher likelihood of having children at some stage in the future than the general
population. The risk of genetic effects is therefore much greater.
The following graph illustrates how the risk of developing radiation induced fatal cancer decreases
with the age at which the person is exposed to radiation at low doses or at LOW Dose Rates for a UK
population.
Note: The population-weighted average is 5.8 % Sv -1
for males and 5.9 % Sv -1
for females
Reference: NRPB (1993) “Estimates of Late Radiation Risks to the UK Population”. NRPB Volume 4, No. 4.
Risk of Genetic Effects
At diagnostic levels of doses, the risk of passing on a genetic effect is judged by the NRPB to be
small relative to the natural risk of genetic disease.
Reference: NRPB. (1993). “Board Statement on Diagnostic Medical Exposures to Ionizing Radiation During
Pregnancy”, Volume 4, No. 4
Risk Categories When considering the acceptability of risk the ICRP takes into account the probability of death or
severe hereditary effect, and in addition considers the length of life lost and the incidence of non-fatal
effects.
ICRP also find it useful to categories the tolerability of risk into three groups:-
• Unacceptable (Risk not justified)
• Tolerable (Risk ALARP)
• Acceptable (Negligible risk)
Comparative Common Risks
The risks can also be compared to the risk from certain everyday activities. For example, every year
there is 1 in 10,000 risk of dying as a result of a road accident and 1 in 200 risk of dying as a result of
smoking 10 per day. In Book 4 these risks are compared with the risks from various diagnostic
techniques involving ionizing radiation.
Radiation Accidents
Everyone is aware of the fatal consequences of a radiation accident like the one that happened at
Chernobyl in 1986. However, a number of other less well known accidents, some fatal, have in many
cases given rise to localized skin damage or varying degrees of radiation sickness.
This book has given you an outline of the mechanism leading from radiation exposure to biological
effects, and has attempted to put the risks of such exposure in relation to other risks we have to face
in life.
Book 4: Aims of Radiation Protection
In book 3, the risk of stochastic effects to patients from the doses and dose rates encountered in
diagnostic radiology was discussed.
This book will now consider:
• Why patient dose reduction is important.
• What can be done by doctors to reduce patient doses?
• What are the legal implications of patient dose reduction?
Note: Throughout this book the term “dose” should be taken to mean effective dose
Imaging Techniques
This book will begin by looking at the different types of diagnostic imaging techniques which
involve ionizing radiation, for example X-ray imaging and CT scanning.
The range of doses which are received by the patients from these various techniques will be
considered. Consideration will also be given to some alternative imaging techniques which do not
involve the use of ionizing radiation, for example Ultrasound imaging.
• X-ray projection images display the patterns of X-ray transmission through the patient. This
may be in the form of a hard copy image (radiograph), which is the conventional X-ray
picture recorded on film. Alternatively it may be a fluoroscopic, real time image displayed on
a television monitor.
• Computed Tomography (CT scanning) is an X-ray technique for the production of cross
sectional images of the patient. CT scans provide detailed anatomical pictures in which there
is excellent definition of the tissues.
• Nuclear Medicine is another technique which involves the use of ionizing radiation. In nuclear
medicine a radionuclide is administered to the patient. The pattern of the radionuclide
distribution can then be displayed through the detection of the emitted radiation.
There are alternative imaging techniques which do not use ionizing radiation. Magnetic resonance
imaging (MRI) and ultrasound are both in routine use. The physical process to
Construct these images different from techniques using X-rays. The display of anatomical structure is
therefore different.
Alternative techniques often complement those which use ionizing radiation and sometimes take
place of them. Alternative techniques should be used if possible. The modality chosen will depend on
the clinical situation.
Medical use of ionizing radiation is a large contributor to the overall annual dose to the UK
population:
Data: Hughes JS, and O’Riordan, M C (1993) Radiation Exposure of the UK Population – 1993 Review, NRPB – R263
Importance of Dose Reduction
It is important to reduce the overall dose to the general public from the medical use of ionizing
radiation because:
• It is estimated that unnecessary diagnostic radiology could be responsible for between 100 and
250 of the cancer fatalities in the UK each year.
• It is estimated that the harm done by unnecessary diagnostic radiology is in the region of ₤375
million years.
It is important that you understand the criteria for deciding when to use an investigation that involves
ionizing radiation.
Some imaging techniques involve the use of ionizing radiation and some do not.
You must understand the principles of the imaging methods available to you.
You should know where you can get advice on making clinical decisions such as:
“Do I need an X-ray?”
Consideration of the case in hand, combined with a working knowledge of dose limitation can
eradicate unnecessary exposures. Remember: All doctors have a responsibility for reducing patient
doses, not just the Radiologist.
There are two combining factors to the unnecessary dose to patients form diagnostic radiology:
• The performance of clinically unhelpful examinations. (It has been estimated that approx. 20%
of radiological examination requests are inappropriate and unnecessary).
• Unnecessarily large patient doses from essential radiological examinations.
Reference: “Patient Dose Reduction in Diagnostic Radiology:,
Documents of the NRPB, Vol.1, No.3 London HMSO
Previous Radiograph Availability
Doctors should check whether the patient has had a previous radiographic examination which could
provide the information required for the new X-ray request. In the patient’s case notes there should
be a report for every X-ray examination that has been carried out previously. The films are retained
in the Radiology Department.
• As the patient if they have had any recent X-ray examinations.
• Check the patient’s case notes
If a patient transfers to another hospital, the case notes and therefore the radiological records should
be transferred also. The original X-ray should be made available if required. It has been estimated
that in some hospitals as many as 30% of investigations are unnecessary repeats because the previous
study has been lost.
Reference: “Patient Dose Reduction in Diagnostic Radiology”, document of the NRPB, vol. 1, No. 3,
1990, London HMSO, and “Unnecessary X-ray examinations”, M.A.P. Bransby-Zachary, and G.R.
Sutherland BMJ, Volume 298, 1294, 1989
Clinical Justification
It is essential that radiology is only used when the outcome of the investigation is likely to affect
patient management.
If you will take the same course of action regardless of the outcome of a procedure involving
ionizing radiation then you should reconsider the value of that procedure.
Investigations should not be undertaken unless there is clinical justification.
This will greatly help to reduce the number of unnecessary exposures to diagnostic radiation.
Dose Justification
A booklet, “Making the Best Use if a Department of Clinical Radiology – Guidelines for Doctors”
has been produced by a Royal College of Radiology Working Party. This is essential reading for all
doctors and can be obtained from:
The Guidelines Secretary, royal College of Radiologists,
38 Portland Square, London WIN 4JQ, priced ₤3.50
The purpose of the booklet is to help doctors working in hospitals and primary care to select the most
appropriate imaging investigations for their patients. It will also make for a reduction in radiation
dose and better clinical practice.
The Royal College of Radiologists booklet gives some general indication of which investigations are
justifiable for a range of symptoms. It is not intended to replace clinical expertise but it does assist a
referring clinician in selecting a valid and justifiable investigation.
It is essential that a balance is struck between the risks and the benefits associated with a procedure
involving the use of Ionizing Radiation.
The use of ionizing radiation must produce a net benefit to the patients’ health.
Risk Assessment
It is important to assess the level of risk that is acceptable for medical diagnosis in each patient.
Obviously, the more serious a patient’s illness then the greater the acceptable risk becomes.
However, even when a patient is seriously ill you do not use ionizing radiation unless it will provide
essential information for patient management. Imaging should only be used when it is likely to
change a patient’s course of treatment.
How much Ionizing Radiation?
The doses associated with the various diagnostic investigations involving Ionizing Radiation range
from 0.01mSv to 20mSv. You do not need to know the dose for every procedure, however being able
to compare frequently used examination is essential.
You must be aware of the recommendation for the use of ionizing radiation and some of the
principles of radiation dose optimization.
These factors will be discussed in the rest of this book.
X-ray Procedures
This table shows typical X-ray dose values for a range of procedures:
The data was completed during a survey of UK Hospitals.
Dose Levels
The magnitude of the doses involved in the various X-ray examinations can be compared by
considering the equivalent number of chest X-rays to give the same dose.
This shows in the table below:
Nuclear Medicine Procedures
This table shows typical doses received in some nuclear medicine studies:
The data for X-ray and nuclear medicine doses was extracted from: RCR Working Party. Making the Best Use of a
Department of Clinical Radiology: Guidelines for Doctors (Third Edition). London: The Royal College of
Radiologists, 1995 © the Royal College of Radiologists, and Notes for Guidance on the Administration of
Radioactive Substances to Persons for Purposes of Diagnosis, Treatment of Research, ARSAC, January 1993
Collective Dose form Diagnostic Radiology
X-ray of the chest, limbs and joints and dental X-ray are carried out with the greatest frequency as
can be seen from this pie chart. (The data is for the UK in 1992):
However, it is a very different story if the doses from these examinations are considered. It can be
seen from this pie chart that the contribution to the Collective Dose to the population is actually
greatest from Computer Tomography (CT), Lumbar Spine X-rays, Barium Enemas and Barium
Meals as the following chart shows.
The dose imparted from Computed Tomography (CT) is high and should be minimized.
In recent studies, the contribution of CT to the collective dose from all X-ray examination has
increased to a third and is probably still rising.
Reference: “National Protocol for Patient dose Measurement in Diagnostic Radiology”, prepared by the
Dosimetry Working Party of the Institute of Physical Sciences in Medicine, NRPB, 1992
Lifetime Cancer Risk from Medical Examinations
In Book 3, it was discussed how the risk of developing fatal cancers from radiation doses could be
assessed using models established from the study of Japanese atomic bomb survivors and other
groups of people who were irradiated to high doses. The risk of developing a stochastic effect from a
radiation dose received for particular medical examinations can be assessed. It is estimated that for
every million patients, a certain number may develop a fatal cancer, depending upon the examination
involved. The younger the patient the higher the risk .
The figures in the following table were calculated using the NRPB figure for risk of developing a
fatal cancer = 5.9% per Sv and by using typical effective doses for the medical examinations from
the RCR Guidelines:
These “lifetime” risks can be compared with the “annual” risks of death in everyday life which were
discussed in Book 3. For example, at the age of 40 there is a 1 in 700 (1,400 in 1,000,000) annual
risk of dying of natural causes and there is a 1 in (10,000,000) annual risk of dying as a result of an
accident in the home. The lifetime risks of these common causes of death can then be found by
summing the age specific risks for each remaining year of life.
Data Calculated from:
• Average Effective Doses, Hughes, JS, and O’Riordan, M C (1993) Radiation Exposure of the
UK Population – 1993 Review. NRPB – R263.
• RCR Working Party. Making the Best Use of a Department of Clinical Radiology: Guidelines
for Doctors (Third Edition). London: the Royal College of Radiologists, 1995
• NRPB Figure for Risk – The data was extracted from: SRP, Journal of Radiological Protection,
Volume 14, No. 1., 1994
Legal Limits?
There are legal limits for the doses received by radiation workers and the public; however
there are no limits to patient doses administered in radiology.
The NRPB and the RCR have instead published reference doses for a range of procedures, to be used
as guidelines for good practice.
Dose Optimization.
The basic principle for dose optimization in radiation protection is “As Low As Reasonably
Achievable”. The dose administered to a patient must be as low as reasonably achievable without
compromising the diagnostic results. The phrase “As Low As Reasonably Achievable” was coined
by the International Commission on Radiological Protection (ICRP) in 1997. ALARA is the basic
principle underlying the Ionizing Radiation Regulations 1985 and the Regulations in the UAE. It
takes into account economic and social factors.
Sometimes the term ALARP is used and this stands for As Low As Reasonably Practicable
Reference Doses A national patient dose survey was carried out by the National Radiological Protection Board
(NRPB) in the 1980s and as a result of this; the NRPB has recommended Reference Dose Levels for
particular X-ray examinations.
Dose Constraint
If department find the mean doses they record exceeds the reference levels then they should
immediately investigate the reasons for their excessively high doses. Steps can then be taken to
ensure that procedures are optimized in order to reduce the dose to patients, for example, by making
changes in techniques or by investigating in new equipment.
The maximum expected radiation dose which may be given to carry out a procedure involving
ionizing radiation and is known as the dose constraint for that procedure.
Reference Dose levels may be considered as a dose constraint in Quality Assurance.
Aim of Quality Assurance
A Quality Assurance (QA) program in a diagnostic imaging department has been described as an
organized effort by staff to ensure that the diagnostic images produced are of sufficiently high quality
so that they consistently provide adequate diagnostic information at the lowest possible cost with the
lowest possible dose to patients.
A full QA program needs to be wide ranging to cover such things as staff performance (radiographer,
radiologist, nursing and clerical), radiology interpretation, radiographic practice, equipment
performance, audit of patient doses and value for money to name but a few.
Three aspects of a QA program will now considered in detailed:
• Film Reject Analysis
• Quality Control (QC) of equipment
• Regular Patient Dose Monitoring
However, remember that these three aspects form only part of the wide ranging Quality Assurance
program that should exist within a department.
Film Reject Analysis
Performing Film Reject Analysis
It is inevitable that some radiographs or nuclear medicine images will not be of diagnostic value.
Critical examination of these rejected images can make possible identification of problem areas, for
example one individual who is not carrying out a procedure correctly or an equipment fault.
Corrective measures can then be introduced.
Quality Control Equipment
Each department should operate a Quality Control program which will involve periodic checks on
the performance of equipment that generates measures and/or handles radiation. In a radiology
department, routine checks will be performed by the radiographers and possibly by the radiologists,
while longer term checks will be carried out by members of the medical physics department and
possibly by the manufacturer.
Regular Patient Dose Monitoring
Radiology Departments and Nuclear Medicine Department should systematically measure and record
patient doses, which can be against the recommended Reference Dose levels.
The patient dose from an X-ray examination can be calculated or measured using:
• Thermo luminescent dosimeters (TLDs) attached to the patient’s skin.
• Patient exposure monitoring devices such as dose area product meters which can be built into
X-ray machines.
QA Cycle
The data which is gathered during AQ, for example the data on patient doses can be audited to check
the performance of the department. Problem areas may be identified and changes can be made.
Much Higher Than Intended
One particular requirement of this Core of Knowledge course is to know to deal with a case of
“overexposure”, i.e. if due equipment faults, breakdown in procedures etc., a patient is given a dose
that is MUCH GREATER than intended when compared with the ‘normal’ practice for a particular
procedure in a particular department.
If the actual exposure is greater than that intended by more than the “Multiplying Factor” in the
following table then it is said to be an overexposure”. (Reference: PM77, HSE)
For example, with a Nuclear Medicine procedure that normally gives dose of less than 0.5 mSv, a
dose 20 times larger than was intended would be in this category.
To identify cases of overexposure, you should:
• Be aware of the normal range of doses that are received for a particular examination.
• Be aware of how over-exposures may arise.
• Be aware that other health professionals, such as radiographers who are operating equipment
may notify you of any possible overexposures.
When a suspected over-exposure occurs the following actions should take place:
1) The cause and extent of the incident should be investigated and the number of patients
involved should be noted.
2) The Radiation Protection Supervisor for the department should be notified.
3) The RPS will notify the Radiation Protection Officer (RPO), Clinical Director etc. if
necessary.
4) If in the professional judgment of the RPO the exposure is “much greater than
intended”, it may be necessary to notify competent authority in the UAE.
Book 5: Safe Use of X-rays
In this book you will learn:
• Factors which influence patient dose.
• The procedures which you should follow to minimize patient and staff dose.
• Some guidelines for filling in an x-ray request form.
Although there are many potential areas for patient dose reduction the major factor arises from the
initial clinical decision to X-ray. Once this decision has been justified you must then make sure that
you do everything within your power to minimize the dose.
In this book you will see what considerations you must make before requesting an X-ray.
You will also learn what factors you can influence when performing an X-ray.
Factors Affecting Patient Dose
We must consider the factors in the X-ray imaging system which can be influenced while taking
radiographs. We will consider each factor in turn, concentrating on the more important factors which
may be under your control.
X-ray Parameters
The main factors which influence the dose to the patient are the number of X-ray photons emitted
from the set and the energy of those photons. These are in turn dependent on two X-ray parameters.
• The kilo voltage (kVp)
• The tube current (mA)
The kVp and mA must be carefully selected to ensure that the dose is as low as reasonably
achievable yet with sufficient image quality and diagnostic information. The greater the energy
(kVp), the lower the image contrast, but also the lower the patient dose.
KV and mA are selected to provide an optimum intensity of X-rays reaching the imaging device.
Increasing the kV will increase the intensity at the film so that the mA has to be reduced to
compensate and vice versa.
Low kV (with high mA) generally produces improved image quality but it is the cost of increased
patient dose. Optimum kV settings for radiography are selected by radiographers in line with good
practice.
The mA and exposure time are then set by the radiographer using their experience or an automatic
switch off is used when the right amount of radiation is detected at the film. In most cases the
machine used will set the kVp and mA automatically (Automatic Exposure Control). The
manufacturers of the machines will have calibrated the optimal exposures for each machine. In cases
of older technology, when the X-ray set does not have an automatic exposure setting, exposure charts
will be available for determining the kVp and mA used for standard examinations.
X-ray Field Size
The dose to the patient is also dependent on the volume of tissue irradiated. You can do little to
reduce the thickness of the patient but you can make sure that only the areas essential to the image
are irradiated.
There are two methods of reducing the volume which you irradiate:
• Beam Collimation
• Patient Shielding
Beam Collimation
You must ensure that the beam from the X-ray machine is collimated so that it is only big enough to
irradiate the area of the patient that you are trying to image.
It can be seen that the area irradiated when the beam is uncollimated is considerably bigger than
when the beam is collimated to irradiate only the area under investigation. Remember that
collimation has an added advantage of reducing scattered radiation thus improving overall image
quality and at the same time reducing staff dose.
Patient Shielding
Even when the X-ray beam has been collimated certain sensitive oranges may be within the field of
the beam or close enough to be irradiated by scattered photons. In such cases it is advisable to shield
areas of the patient from these X-rays. Leaded shields are available in the Radiology department for
this purpose. Particular occurrences are Gonad shields and Organ shields.
Duration of the Exposure
The dose to the patient increases linearly with the time the patient spends in the beam (for set mA
and kV). It is vital that you try to minimize the time the patient spends in beam.
In fluoroscopy it is important to combined good technique with appropriate use of technology to
minimize the duration of the exposure. Such factors which you can influence include:
• Screening time
The most important thing to remember for the reduction of screening time is that you
do not screen the patient unless you are looking at the monitor. Do not screen the
patient unless you are looking at the image.
• Use of Pulsed Fluoroscopy (when available)
Pulsed fluoroscopy is an innovation which means that the X-rays are on for only a
few milliseconds in each second. Using this feature is very much like obtaining
instant radiographs. The use of this feature will depend on the investigation being
performed. Pulsed fluoroscopy is suitable for imaging static events or slow
movement. Continuous screening should be used for monitoring movement in
investigations such as the insertion of a catheter.
• Use of the last image hold facility –
When operating with this feature you need only irradiate the patient for enough time
to generate an image. The image can then be retained in “memory” whilst the image
is assessed on the TV monitor.
The first of these is reliant on technique. The later options involve making use of the latest
technology to reduce patient dose.
Patient Positioning
There are two factors to consider when trying reducing dose through patient positioning:
• Patient to Image Intensifier distance
• Focus to Skin Distance (FSD)
Both factors depend upon radiation intensity decreasing according to the “inverse square law”. With
few exceptions, it is important that you MINIMISE the distance between the patient and the image
intensifier or intensifying screen. This will also maximize the FSD.
Optimized Viewing Conditions
To make the most of any radiographic examination or procedure the image must be viewed under
optimum conditions. In conventional radiography all radiographs must be viewed on proper viewing
boxes. These provide even lighting and fully illuminate every detail. Important pieces of clinical
information may be missed if a radiograph is viewed unsung a window or a lamp as a light source.
Other factors Affecting Patient Dose
So far we have considered factors which you can influence on a day to day basis. There are other
factors which influence patient dose. These are dependent on the type of equipment being used in the
department. The main factors are:
• The Sensitivity of the Imaging System
• Attenuation of materials in the beam, such as the cassette cover and the table top.
Reducing Staff Dose
There are few simple precautions which you should take to minimize your own dose whilst
performing radiographic procedures. It is also worth remembering that anything you do to reduce the
patient’s dose will also reduce your dose.
Staff Dose Reduction (Procedural)
• Never put your hands in the X-ray beam.
• Remember that your dose is from scattered radiation off the patient, therefore, standing beside
the X-ray machine will not reduce your dose! The dose from scatter is at its highest at the
beam entry point to the patient.
Stand as far away from the patient as is consistent with performing your duties. By doubling the
distance between yourself ant the X-ray source you can quarter your dose (Inverse Square
Law).
• Use sets with under couch geometry i.e. the X-ray tube is below the couch and the image
intensifier is above the couch.
• When the tube is under the couch, the point of maximum scatter is under the patient. Much of
the scattered X-rays will be directed downwards. Some of the scattered X-rays moving
upwards will be attenuated by the patient.
• When the tube is above the couch, the point of maximum scatter is top of the patient thus many
of the scattered X-rays are directed towards the operator.
• When performing lateral or oblique views stand beside the image intensifier whenever possible.
Staff Dose Reduction (Equipment)
• You should stand behind a protective screen unless your presence in the room is essential.
• If you need to be in the room wear a lead apron and fasten it securely.
• If you have been issued with a dose monitor always wear it when working with radiation. This
enables the dose which you receive to be monitored for irregularities. Note: if a lead apron is
worn such monitoring devices should be worn underneath the apron in their normal position.
Dose monitors should be worn whenever convenient between chest and waist.
• Wear protective clothing such as thyroid shields and leaded glasses when instructed to do so by
the Radiation Protection Supervisor (RPS). Generally this is only necessary for high dose
interventional procedures and x-ray equipment with unprotected geometry.
• Observe the warning lights outside X-ray rooms.
• Use ceiling mounted screens or other types of local shielding if available.
Requesting Radiographs
Before filling in X-ray request forms check if the patient has already had a pertinent examination,
which may provide the information that you require.
• Ask the patient if they have had any recent X-rays.
• Always remember to check the patient’s records to see if they have been X-rayed previously.
An important factor when filling in an X-ray request form is which views will be clinically helpful?
There are guidelines for good practice published in the RCR Guidelines. Your radiology department
may have their own “in-house” guidelines. These must be treated only as guidelines; they are not
replacement for clinical expertise. There must be good reasons for ignoring the guidelines but you
must consider the needs of the individual patient.
You will rarely have control over which radiology departments you send your patients to. You must
be aware, however, that the dose for a particular examination may vary in different departments due
to variation in equipment and operating procedures.
If the examination is one which would deliver a significant dose to the fetus you should ask the
patient if they COULD be pregnant before filling in an X-ray request.
Stochastic effects, e.g. Childhood Cancer, have no Dose Threshold and may be included by the low
doses associated with diagnostic radiology. However, the exposure of a fetus to such a dose of
ionizing radiation is unlikely to result in a deterministic effect such as a birth abnormality. This
subject is covered in depth in Book 7.
Once you have decided to request an x-ray, you should consider this advice from the RCR, who take
the view that”…a request for a radiological examination is a request for an opinion from a clinical
radiologist in the form of a report to assist in the management of a clinical problem. Request forms
should be completed accurately and legibly to avoid any misinterpretation, should state clearly the
reasons for the request and give sufficient clinical details to enable the radiologist to understand the
particular diagnostic problems that you are attempting to resolve by radiological examination”.
Furthermore, you must take into account other factors that may influence the procedure:
• Consider the urgency of the investigation
• Is an out-of-hours request necessary?
• Is mobile X-ray necessary?
Sign the Request Legibly
Most request are for investigations which involve ionizing radiation and therefore carry an associated
hazard for the patient. The request should only be signed by the requesting clinician when the
decision to irradiate is made.
Furthermore it is important that the radiology department can read who is requesting the
investigation. To this purpose you should sign your name legibly. It may also be useful to print your
name and your bleep number beside the signature. This information enables the radiology
departments to clarify any necessary details without delay.
Make Sure the Patient Details are Correct
Make sure you supply the correct patient details. We must make sure that the investigations are
performed on the correct patient! Age and sex can also affect diagnosis.
Make sure that you supply the location from which you are making the request; otherwise the
radiologist will not know where to send the report.
Clinical Details
Radiographers need to know the clinical context within which they are performing an investigation.
Radiological signs can be non-specific and can result from more than one pathological process. If a
radiologist does not have sufficient clinical information then the information supplied by the
investigation may be misinterpreted.
Book 6: Safe Use of Radionuclides
Nuclear Medicine is the branch of medicine involved in using radionuclides for diagnosis and
therapy. In this book you will learn:
• About the use of radionuclides in nuclear medicine procedures.
• What things you should consider when requesting a nuclear medicine study for a patient and
how to request such a study.
• How to handle radionuclides safely, in order to protect both patients and staff.
Diagnosis and Therapy
Radionuclides are used for both diagnostic tests and therapeutic purposes.
Diagnostic tests allow the function and/or structure of most organs in the body to be assessed. In
therapeutic procedures, radionuclides are targeted to a group of cells within the body in order to treat
cancers or reduce the function of an organ.
The doses that are given for diagnostic tests are much lower than the doses that are given for
therapeutic purposes.
Radiopharmaceuticals
In most of these tests, a pharmaceutical is labeled with a radionuclide such as Tc 99m, resulting in a
radiopharmaceutical, which can then be injected into the body.
The choice of pharmaceutical is dependent upon the organ that a particular diagnostic test is intended
to image, or the organ that a particular therapeutic technique is targeting. For example, because
functional thyroid cells accumulate and trap iodine, nuclides of iodine are used to target the thyroid
gland for both diagnostic and therapeutic procedures.
Radionuclides for Diagnosis
Radionuclides used for diagnostic tests typically emit gamma radiation. Once the
radiopharmaceutical is administered to the patient, the long range of the gamma radiation allows its
distribution to be imaged from outside the body using a gamma camera.
Radionuclides for Therapy Radionuclides used for therapy are beta emitters and hence when they accumulate in the target organ
the beta rays deposit their energy in a very short range killing some of the tissue.
What is Nuclear Medicine?
The following types of nuclear medicine investigations are carried out:
• Imaging Investigations-
Diagnostic tests involve imaging the patient directly using a camera such as a gamma
to obtain either still or moving images of the distribution of the radioactivity within
the body. Examples are: static bone scan images, static DMSA kidney scan and
dynamic DTPA kidney scans.
• Non-imaging investigation –
Other diagnostic tests are non-imaging and involve administering a
radiopharmaceutical to a patient in the form of an injection or as a drink. Samples are
then taken from patients and the distribution of the radionuclides can be measured by
either Blood tests, Urine tests, Whole body counter or Surface counter. The
quantified radionuclide distribution gives information about the rate of clearance of
the radiopharmaceutical from the body or the volume of a compartment within the
body e.g. blood volume, which can then be used for diagnostic purposes.
• Therapeutic procedures –
Therapeutic procedures which might be carried out in nuclear medicine involve the
administration of high dose radionuclides. These can be in solid, liquid or gaseous
forms.
ALARA
With all these procedures, the exposure to radiation should be kept As Low As Reasonably
Achievable and no procedure should be carried out unless it is justified.
In general, the activity administered to a patient will not be greater than that indicated in the Basic
Regulations for the Protection Against Ionizing Radiation issued by the Ministry of Water and
Electricity, UAE, 2004.
If there is a choice of procedures available which give the same result, use the one which gives the
patient the least radiation dose.
Requesting
Nuclear medicine tests are often referred to as “scans”, “isotope studies” or “radionuclide imaging”.
When requesting a study, indicate clearly which imaging method is required e.g. Dynamic plus static
bone scan. Don’t simply ask for a “scan”.
Appropriate clinical details should be written on the request form to ensure the correct procedure is
carried out.
Other details such as the patient’s weight may be required on the request form. For example, in the
case of pediatrics the child’s weight may make a difference to the dose that is given. The request
form acts as a prescription for the administration of the radionuclide and hence must be signed by a
medically qualified member of staff on behalf of the consultant requesting the scan.
In What Order Should Tests be given?
If a patient needs several radionuclide investigations, the radioactivity from one test may interfere with another test. It is best to discuss the order in which the tests are carried out with Nuclear Medicine staff before making arrangements for scans. For example, if a patient needed a scan using a long lived isotopes such as Se75 and a scan using
Tc99m, it would be best to do the Tc99m test first as it takes a long time for the Se75 to decay away
and residual Se75 would cause problems with subsequent scans.
Consideration must also be given to non-Nuclear Medicine investigations.
Ensure that other investigations, especially those which involve a long period of close contact with a
patient are not organized for the patient directly after an isotopes injection as this is exposing the staff
out these procedures to an unnecessary radiation dose e.g. an ultrasound should be arranged before
the injection is given or on different day.
Avoid Repeats
Avoid repeating scans by checking if the same scan has been carried out or requested recently by
another clinician.
Risk
It is helpful to be able to assess the risks of inducing cancer in a patient from a particular procedure.
In Book 4 the risks from certain Nuclear Medicine procedures were compared with the risks from
certain everyday activities and to risks from some-x-ray procedures.
Patient Preparation
It is important that the patient undergoes the correct preparation prior to a test to ensure that the
correct diagnosis is established and to avoid repetition of the scan.
Preparations for some Nuclear Medicine scans could include:
• Fasting,
• Changing or interrupting existing drug therapy,
• New medication associated with the scan may have to be taken.
To avoid patients getting unnecessary doses:
• The patient should be reviewed early in the morning if it is suspected that they may not be well
enough on the day of the scan
• The patient is likely to be un co-operative, leading to them not lying still for the scan, make sure
they have had appropriate sedative or painkillers so that the study does not have to be abandoned.
Pregnant and Breastfeeding Patients
Particular risks to pregnant and breast feeding patients should be considered.
These are discussed in Book 7.
The Radio pharmacy
In most hospitals the radiopharmaceutical will be made up in the radio pharmacy department to the
correct activity and volume and this will then be delivered to the ward or the Nuclear Medicine
Department where it is to be administered to the patient. In other hospitals the doctors may be
expected to sub-dispense and to measure out the radiopharmaceutical.
Handling Unsealed Sources
The isotopes for these studies are unsealed sources of radionuclides which can exist in tablet form, as
a solid, as liquid or as a gas.
If you are handling these it is important to remember that the radioactive material can enter your
body in three ways:
INGESTION via the mouth,
ABSORPTION via the skin, or,
INHALATION via the lungs
Precautions: Distance, Shielding, Time
To protect both patients and staff, it is useful to remember the “Distance, Shielding, Time” rule when
handling radionuclides.
DISTANCE:
Keep sources at a distance by holding them at arm’s length and only having those people in
the room that are necessary. If you are holding a syringe hold it by the plunger part which is
furthest away from the radioactive solution.
If necessary, remind yourself of the Inverse Square (refer to the Glossary).
SHIELDING:
Shielding on sources is there to protect you. Syringes containing sources that are emitting
gamma rays will have a lead shield around them to reduce the radiation dose to the fingers.
This shield is normally 2 mm thick and can reduce the gamma radiation emitted by the
radionuclide technetium-99m by up 90%. Keep your fingers behind shielded areas around
syringes etc. Keep any sources shielded as long a possible. If there is shielding on an
injection syringe do not remove it.
TIME:
Time is of the essence. Plan what you are going to do beforehand so that you can spend a
minimum time actually handling the source. The shorter the time spent in the vicinity of the
source, the smaller the dose. Explain everything to the patient prior to the injection to
minimize the contact with the patient afterwards.
Administering Radiopharmaceuticals
The MAJORITY of radiopharmaceuticals are given by intravenous injection.
The precautions that are necessary when giving these injections will now be discussed.
Radiopharmaceuticals can also be administered in the form of drinks or tablets or they may have to
be breathed by patients.
You will need to be trained in the particular techniques that are necessary if you are to be involved in
administering radiopharmaceuticals by these methods.
Precaution: Patient Identification
Before administering a radiopharmaceutical:
Check that you have the correct patient by asking the patient to state his or her name and date of
birth. It is not adequate to state the patient’s name and date of birth and ask if they are correct,
patients have been known to answer to the wrong name! Double check the patient details with the
request form if it is available.
If appropriate, check that the patient is not pregnant or breast feeding.
If the wrong patient is given a radiopharmaceutical injection then the consequences of this are firstly
that the patient receives an unnecessary radiation dose.
Also, this radioisotope injected may then interfere with the test they are intended to get which might
then have to be postponed.
If a patient is given an incorrect radiopharmaceutical injection, then this MUST be reported to the
Radiation Protection Officer (RPO) and the Head of the Nuclear Medicine Department immediately.
Precaution: Checking Scan Details
There may be precautions which have to be taken when injecting a pharmaceutical depending upon
the particular diagnostic test that is being performed.
To be sure of any precautions; ALWAYS read the instructions which have come with the
radiopharmaceutical injection.
Expelling Air
With the exception of the lung perfusion study there should be no need to expel air from the syringe as this will have been done when the injection was prepared. Precaution: Injection Time
You may remember from Book 1 that all radioactive substances have a half-life and therefore their
activity is constantly changing. In order to achieve a good imaging result from a
radiopharmaceutical, the injection time will have been calculated precisely and it is important that
you ensure that the injection is given at the specified time.
If it is given too early the patient may receive an unnecessarily high dose.
If it given too late there may not be enough time for the radiopharmaceutical to distribute to
achieve a good diagnostic image.
The injection time will be written on the label that arrives with the radiopharmaceutical injection.
The aim is that the injection should be given at the time stated on the label. This isn’t always possible
so it is very important to record the exact time of the injection for correct analysis of results.
Check with Nuclear Medicine if you are unsure.
The person who administers the radionuclide must sign the injection box and the time of
administration should be recorded.
Precautions: Avoiding Spillages
Injections of radiopharmaceuticals should be given in a clear, uncluttered area.
• The area should be uncarpeted so it is easy to clean up a spill if necessary
• Place a disposable and absorbent material under the patient’s arm to catch any spills e.g. an
incontinence pad.
• The person giving the injection can be protected by wearing gloves and a closed white coat
to avoid contaminating the skin in the event of a spill.
Precaution: Avoid Extravasation
When injecting a radiopharmaceutical, it is particularly important to ensure that it goes into the vein
and is not Extravasation (tissue|). A butterfly can be used to ensure this. When a patient is to be given
a series of injection a venflon should be use.
If however, you do extravasation an injection this should be immediately reported to the Head of
Nuclear Medicine.
Evidence of Extravasation
In the following image of a bone scan, the radiopharmaceutical has been extravasated and shows up
as a dark area where it was injected near the elbow.
The image is of poor diagnostic quality because only a small amount of the radiopharmaceutical has
been taken up in the bones and the ribs are not easily identified.
Consequences of Extravasation
It the radiopharmaceutical is extravasated, the possible consequences are:
For a few tests it may still be possible to go ahead and scan the patient and get a result.
However with other tests, the quality of the results will be compromised and another isotope
injection may be required (possibly after a delay of several days).
If certain injections containing beta emitters are extravasated, the ionization will be highly
localized and can result on skin necrosis.
After the Injection
When the injection has been given, it is important to dispose of the radioactive syringe and needle in
the correct manner. Remember that they are radioactive. DO NOT DISPOSE OF THEM IN THE
SHARPS BIN ON THE WARD. They will probably have to be returned to the Nuclear Medicine
Dept. in the container in which they arrived. Once you have finished handling injection materials,
remove your gloves using the surgical technique and place them with the radioactive waste.
You should then wash your hands.
Spillage
In the event of a spillage occurring, restrict access to the area, and if available, drop tissues on it to
stop it spreading around the ward. Then immediately contact the competent person(s) referred to in
your local rules who will deal with such an occurrence e.g. the RPO or the Nuclear Medicine
Department. Note: Patient care is always the first priority.
In the case of LARGE spills:
Contact the Nuclear Medicine Unit IMMEDIATELY
In the case of small spills:
Inform the Nuclear Medicine Radiation Protection Supervisor so that, if necessary, they can
check for any residual contamination and they can remove contaminated materials so that
they can be stored until the activity has decayed.
Dealing with spills on skin:
If there is a spell on the skin, firstly soak up the excess liquids using absorbent material and
place all tissue material in a plastic bag.
Any residual contamination can then be removed by washing the skin thoroughly with soapy
water.
Dealing with spills on clothing:
Clothing should be removed as soon as possible and any soiled clothing should be placed in a
plastic bag.
Dealing with spills on floors or other surfaces:
Contain the spill do not spread it, restrict access to the area, use absorbent material to soak up
liquid and place in a plastic bag.
After Care of Patient
Once a patient has had a radioactive injection, they can be considered as radioactive and all body
fluids will be slightly radioactive. Any spill of urine, vomit or any body fluid should be thoroughly
washed from the skin and cleaned from floors etc. as is normal for biohazard. If it is unavoidably
necessary for blood or urine tests to be carried out then ensure that the container is marked with a
radioactive sticker and explain to the laboratory that specimens may contain small amounts of
radioactivity so that they can take necessary precautions.
Care of Patients given Therapeutic doses There are particular precautions which are necessary when patients are given the very high doses
associated with therapeutic injections of radiopharmaceutical.
Protective gloves should be worn when handling the vomit/urine from patients who have
received certain therapeutic doses.
It may be necessary to isolate patients who have therapeutic doses of radiopharmaceutical for
a short time until some of the radioactivity has cleared from their system.
Visiting by family members may have to be restricted to very short length of visit.
An instruction leaflet will usually accompany each patient who has received a therapeutic dose of a
radiopharmaceutical. This will normally state how long to apply any special precautions concerning
contact with other persons
Pregnant Members of Staff
Pregnant staff or pregnant members of the public should avoid contact with patients at the time of
injection and on the day of the scan.
After Care of Breastfeeding Patients
If a patient is breastfeeding her baby, the main precautions are that the patient may be advised to
interrupt breast feeding for a short period or to stop breast feeding altogether as the
radiopharmaceuticals can be excreted in breast milk. The advice that is given to a patient is
dependent upon the radiopharmaceutical that has been used in the test which they have undergone.
There will be more information about particular precautions for pregnant and breast-feeding patients
in Book 7.
Book 7: Radiation and Pregnancy
Radiation to the developing fetus and to children has an increased potential for harm. It is an issue of
particular concern both to pregnant patients and to staff.
This book will answer the following questions:
What are the radiation risks to the fetus?
What are the implications for pregnant staff?
How can inadvertent exposure of the fetus of a pregnant patient be avoided?
What advice should be given following the radiation exposure of a pregnant patient?
In this book, the radiation dose to the fetus is quoted in grays rather than Sieverts. The reason for this
is that the fetus has been considered as an organ of the mother’s body and the Absorbed Dose to
single organs is normally measured in grays. Remember that for gamma radiation and x-rays which
have a Radiation Weighting Factor of 1, 1 Gy is equal to 1 Sv.
Radiation Risks to the Developing Fetus
We have already seen in book 3 that radiation effects may be classified as deterministic or stochastic.
In general, in utero doses have no implications for deterministic effects in an individual pregnancy.
This is because, in practical terms, the threshold doses for the induction of effects such as death or
gross malformation following in utero radiation expose lie well above the mean doses that arise from
MOST diagnostic radiology examinations.
Threshold Dose
This threshold dose could only be exceeded if the patient is undergoing multiple examinations. The
maximum recorded fetal doses from barium enemas or pelvic CT procedures only approach this
threshold dose.
If a patient was undergoing such examinations, this would imply that the degree of ill health or injury
that she was suffering might in itself seriously jeopardize the pregnancy.
Radiation Risks to the Developing Fetus
However, you SHOULD be concerned with possible stochastic effects. This is because even the low
doses given in diagnostic procedures could lead to a stochastic effect. The reason for this being that
Stochastic effects have no dose threshold. The main risk is the development of childhood cancer. It is
this effect which is of greatest significance to patients having diagnostic examinations with ionizing
radiation. Childhood cancer which develops before the age of 15 years can be caused by irradiation
of the fetus. This is a stochastic effect.
For low LET radiations (e.g. gamma and x-rays), the risk factor for the induction of fatal childhood
cancer is 3% per Gy, that is a 1 in 33,000 risk per mGy. This risk may be compared to the incidence
of fatal childhood cancer which is 1 in 1300 in the UK.
Reference: NRPB (1993). “Board Statement on diagnostic Medical Exposures to Ionizing
Radiation During Pregnancy”, NRPB Volume 4, No.4.
Radiation Dose to the Fetus
Typical doses to the fetus from x-ray and nuclear medicine examinations are shown in the Table:
The data was extracted from: NPRB. “Board Statement on diagnostic Medical Exposures to Ionising Radiation during Pregnancy”. NPRB volume 4, No.4., 1993
For x-ray examinations of areas which are remote from the lower abdomen and pelvis, for example
x-rays of the skull, chest or extremities, the x-ray dose to the foetus is low, generally less than 0.01
mGy. For a CT scan of the chest the dose is typically 0.06 mGy.
In nuclear medicine the dose to the fetus arises not only form the uptake of the radionuclide in the
organ under examination. It is also depends on the pattern of uptake in other maternal organs. In
particular many of the radiopharmaceuticals used in nuclear medicine are excreted in the urine
implying a high level of activity in the bladder which is situated close to the uterus. The high fetal
dose arising from a brain scan (4.3 mGy) is an example of this effect.
Pregnancy and Work with Radiation
It is important that female staff that becomes pregnant pay particular attention to the standard
radiation protection precautions. There are special dose limits for pregnant staff. Generally, in
hospitals, no changes in duty are necessary for pregnant staff working with ionizing radiations.
However, there are certain duties involving potentially high radiation doses which should be avoided.
The proposed does limit to the fetus of a female radiation worker (average equivalent dose) is 1 mSv
over the declared term of pregnancy.
The proposed dose limit to the fetus of a female radiation worker (average equivalent dose) is 1 mSv
over the declared term of pregnancy.
The fetus lays several cm below the anterior skin. Due to the attenuation of x-rays in the overlying
tissues, this dose limit corresponds to 2 mSv on the skin or the dose monitor.
In nuclear medicine, in which higher energies are used, the attenuation is less. Therefore the fetal
dose is generally assumed to be equal to the film badge dose in this situation.
Precautions to be taken by Pregnant Staff
A report by the RCR and the BIR “Pregnant and Work in Diagnostic Imaging” was published in
1992. In this report the results of a survey of radiation doses to hospital staff are given. These are
summarized in the table.
It can be seen that only about 3% of radiologists (the group receiving the highest doses) had annual
doses which were greater than 1 mSv. This corresponds to the dose limit to the fetus.
Doses which were greater than 1 mSv. This corresponds to the dose limit to the
fetus.
Percentage of Staff in Dose Interval (%)
Dose Interval (mSv)
Radiologists Radiographers Other Clinicians Scientific/Technical
0.0-0.4 88.4 98.1 98.4 96.1
0.5-0.9 8.4 1.2 1.1 1.7
1.0-1.9 2.4 0.5 0.4 1.5
2.0-5.0 0.6 0.1 0.2 0.6
>5.0 0.3 0.1 0.0 0.1
The report came to the following conclusions and recommendations:
There is no evidence to show that there is any significant risk of radiation effects to the fetus
for staff working in radiology departments.
The most effective method of keeping dose low to all staff to maintain good radiation safety
procedures (ALARA principle) using time, distance to shielding to reduce doses.
Technicians or radiographers working in nuclear medicine should avoid high dose situations
such as the handling of generators and dealing with radioactive spills.
Pregnant staff should avoid examinations using 131-I because of the possibility of dose to the
fetal thyroid.
The decision as whether to allow fetus to be exposed to the very small presumed risk arising
from low-level radiation has to be an individual decision.
Imaging in Pregnancy
Before the mid of 1960s it was not uncommon for x-rays to be taken of women during pregnancy as
part of their obstetric management. It is through studies of cancer deaths in the children of these
women that an understanding of the cancer risks has been developed. It is the work of Alice Stewart
and the Oxford Survey of Childhood Cancer which has contributed most to this work. It is through
the understanding of the radiation risks and the development of ultrasound imaging that x-rays are
now rarely used in obstetrics.
Ultrasound imaging is now used routinely in ante-natal care to assess the development of the fetus.
The technique is non-invasive and is not known to be associated with any risk.
Ultrasound scans of a fetus
NRPB, Estimates of Late Radiation Risks to the UK Population”, NRPB, volume 4, No.4,1993
Pelvimetry
Pelvimetry is an x-ray technique used in the later stages of pregnancy to measure the width of the
pelvic brim. The need for such an examination is relatively rare but it is important for the individual
patient that the dose is kept to the minimum.
CT scanning can be used for this technique. CT is generally associated with high doses. However,
with a very low tube current (mA) it is possible to reduce the dose below that needed for
conventional radiographic techniques. At low mA the picture is very grainy but it is sufficient for the
measurement. This is an example of a situation where the doctor should accept poor image if it is
adequate for the clinical purpose.
Dose Limitation for the Pregnant Patient
A pregnant patient should not be examined using ionizing radiation if the fetus would receive a
significant radiation dose unless the examination is of immediate importance to the woman’s health.
If an x-ray of the lower abdomen or pelvis is to be taken of a female patient, she should be asked
whether she is or might be pregnant. Unless the answer is”no”, clinical justification for the procedure
should be sought from the referring clinician or the radiologists who is clinically directing the
examination.
10-day Rule
The 10-day rule is, in general, NO LONGER USED in radiology in the UK. However, recent advice
form the NRPB indicated that in some circumstances there may be a case for its usage.
The 10-day rule was intended to ensure that no woman who was pregnant would have an
examination which would give a potentially harmful dose to the fetus. The rule is summarized below:
X-ray examinations of the lower abdomen or pelvis of women of child bearing capacity, that are
of no importance in connection with the immediate illness of the patient, should be limited to the
time in which pregnancy is improbable, that is the ten day interval following the onset of
menstruation.
This is because it is recognized as being unnecessarily restrictive. Unless the woman’s period is
overdue, the probability of pregnancy is small. If she is pregnant the risk of harmful effects,
particularly at the earlier stage of pregnancy are small. It is considered that the risk to the woman in
delaying diagnosis outweighs any benefit from the 10-day rule.
Patient who may be Pregnant
The Royal college of Radiologist’s Guidelines offer the following advice with regards to “The
Pregnant Patient”.
Irradiation of the pregnant uterus should be avoided whenever possible, and the prime
responsibility for identifying patients at risk lies with the referring clinician.
Radiology staff will check the menstrual history in patients of childbearing potential attending for
radiography of areas between the diaphragm and knees, or for any nuclear medicine procedure.
The radiologist will consider postponing the examination when the last period began more than
28 days previously unless the patient can state that there is no risk of pregnancy. This is the 28
day rule, which has replaced the formal 10 day rule.
If the radiologist and referring clinician agree that irradiation of the pregnant uterus is clinically
justified, the radiologist will ensure that exposure is limited to the minimum required to achieve a
diagnostic result.
©The Royal College of Radiologists, 1995
In addition, the NRPB say:
“For most diagnostic radiation exposures of the early conceptus the risks of cancer will be small:
however, those few procedures yielding doses of some tens of milligray should be avoided, if
possible, in early pregnancy. When the possibility of early pregnancy cannot be reasonably excluded,
one way of avoiding such risks would be to restrict the use of high dose diagnostic procedures, such
as barium enema, pelvic computed tomography (CT) or abdominal CT to the early part of the
menstrual cycle when pregnancy is unlikely.”
RCR Working Party. “Making the Best Use of a Department of Clinical Radiology:
Guidelines for Doctors (Third Edition). London: the Royal College of Radiologists, 1995
NRPB (1993). “Board Statement on the Diagnostic Medical Exposures to Ionizing Radiation during
Pregnancy”, NRPB volume 4, No. 4.
NRPB Advice The NRPB have issued advice regarding the management of patients who have had a diagnostic x-
ray during pregnancy. In respect of cancer induction, they conclude:
For procedures giving doses up to a few mGy, the risks are acceptable compared to the
natural risk. Therefore exposure of the fetus is not considered to be a reason for termination
of the pregnancy or for the use of invasive fetal diagnostic techniques such as amniocentesis.
For exposure at higher doses (tens of mGy), associated with, for example, pelvic CT, there
may be a doubling of the natural risk of cancer in the unborn child. This level of excess risk
is about one in 1000 and is unlikely to be a reason for the termination of pregnancy or for the
use of invasive fetal diagnostic techniques.
Reference: NRPB, Board Statement on Diagnostic Medical Exposures to Ionizing Radiation during
Pregnancy”. NRPB volume 4, No.4., 1993
Dose limitation for the pregnant patient
For examination sites away from the lower abdomen or pelvis e.g. the chest or skull, the fetus should
not receive any direct radiation dose. No special restrictions need arise in these cases provided that
the examination is well conducted (good beam collimation, properly shielded equipment etc.). The
fetus is only affected by scatter radiation. No restrictions need apply in these cases but the use if
additional shielding for patient who is known to be pregnant will provide reassurance. The following
photograph shows a gonad shield in use:
Estimation of fetal dose
Occasionally a patient who has had an x-ray examination will subsequently realize that she was
pregnant when the x-ray was taken. An estimate of the dose to the fetus should be made by the
Medical Physics Department. This can be used as the basis of advice given to the patient. The patient
should be reassured about the hazards of radiation. The radiation dose from diagnostic x-rays is not
high enough to cause any birth defect and usually it will not lead to any significant increase in cancer
risk in individual cases.
Breast feeding mothers
If a radiopharmaceutical is administered to a woman who is breast feeding her child, there is a risk
that the radionuclide will be taken up in the milk. This could cause an unacceptable radiation dose to
the infant. Mothers who are breast feeding should therefore be instructed to take special precautions
if they have a nuclear medicine examination.
The precautions depend on the type of radionuclide, its activity and the radiopharmaceutical. For
certain studies the advice may only be for her to feed the baby immediately before the study and to
express and discard the first feed following the administration of radioactivity. In other cases she
may be advised to express her milk before the study and to store these feeds in the fridge or freezer
for use during the first day after the study. For studies involving longer lived isotopes such as I-131,
she will be advised to cease breast feeding altogether. These precautions should be carefully
explained to the mother before the examination with sufficient time for her to make arrangements for
feeding and these instructions should also be given to her in written form.
Book 8: Rules and Regulations
In the UAE all medical activities that involve exposing patients to ionizing radiation are governed by
law and a set of legal regulations.
In 2009 a new law came into force and a new organization was setup to administer the law and to set
out regulations and control the use of ionizing radiation throughout the UAE.
The new organization is the Federal Authority for Nuclear Regulation (FANR) and they are
responsible for licensing of all institutions that use ionizing radiation throughout the UAE and for
developing and implementing regulations concerning ionizing radiation.
Of particular importance to medical radiation are the following regulations:
1. FANR-REG-24 Basic Safety Standards for Facilities and Activities Involving Ionizing
Radiation
2. FANR-REG-13 Transportation of radioactive Materials
There are also guides to the above regulations and these are:
3. FANR-RG-006 Transportation Safety Guide
4. FANR-RG-007 Radiation Safety Guide
The purpose of the regulations is to specify the minimum requirements necessary for the protection
of persons against ionizing radiation and for the safety of radiation sources. They are general in terms
and apply to all the various uses of ionizing radiation in the UAE
The UAE Law and the regulations were based upon the ICRP (International Commission on
Radiation Protection) and these recommendations can be found in ICRP 60 and 103.
The Basic Safety Standards issued by the IAEA (International Atomic Energy Agency) serve as a
useful guide for radiation safety standards.
The basic principles of radiation protection put forward by the ICRP are:
No practice shall be adopted unless its introduction produces a net benefit.
The ALARA principle. (As Low As Reasonably Achievable)
The equivalent dose to individuals shall not exceed the limits recommended for the
appropriate circumstances by the ICRP.
These general ideas are expanded in the regulation document 24.
Some terminology used in the Medical use of Ionizing Radiation.
Although there are no specific regulations covering diagnostic radiology, nuclear medicine or
radiotherapy at this time although HAAD is working on this.
Clinically Directing
In the UK the regulations require that every medical exposure should be carried out under the
responsibility of a person who is clinically directing such an exposure in accordance with accepted
diagnostic therapeutic practice.
The person who is clinically directing the exposure in radiology is the person who decides that the
patient should be irradiated. In a hospital this is commonly the consultant radiologist, radiotherapist
or nuclear medicine physician, but may be a cardiologist, dentist, orthopedic surgeon, hematologist
etc.
People other than radiologists who clinically direct procedures include:
Cardiologists undertaking cardiac catheterization
Gastroenterologists or pediatrics who screen tubes or capsules into place, and,
Consultants who hold Nuclear Medicine qualifications so that they can undertake nuclear
medicine procedures themselves.
Such people are clinically directing (and sometimes physically directing) the exposure and are
required to ensure that the exposure is carried out “in accordance with accepted diagnostics or
therapeutic practice”.
Requesting
In general, a person simply requesting a radiological intervention is not seen as being “clinically
directing”.
The person who requested the radiological intervention has requested a clinical opinion from, for
example, a consultant radiologist or nuclear medicine consultant. Such an opinion might be that the
intervention is not required and that a different intervention is more appropriate.
Physically Directing
The person who actually presses the exposure button or foot switch is said to be “physically
directing” the exposure. In diagnostic radiology this person is generally a diagnostic radiographer.
Persons physically directing a medical exposure should select procedures such as to ensure that the
dose to the patient is kept as low as reasonably practicable in order to achieve the required diagnostic
or therapeutic result.
Duty of Employers
It is the duty of every employer of persons physically directed or clinically directing medical
exposure to ensure compliance with the training requirements and to keep records of training
particulars showing the date(s) on which training (qualified as adequate training) was completed.
When appointed to a post in which you are required to clinically/physically direct exposures, you
will need to show your employer proof of your training.
The UK regulations also require employers of persons using radiation equipment to:
Keep records in relation to all radiation equipment.
Ensure that person treating patients by radiotherapy or administering radioactive medicinal
products have available to them the services of an expert who is experienced in the
application of physics to the diagnostic and therapeutic uses of ionizing radiation, for
example a medical physicist.
Organizational Structure at AHS
Within any organization, there needs to be a management structure for ensuring compliance with
UAE regulations.
Radiation safety program at AHS consists of the following elements:
•Radiation Safety Committee o Members include: Radiation Safety Officer,
Representatives from Diagnostic Radiology, , Nursing, Administration,
Biomedical Engineering, Medical Physics, Medical Doctor
• Radiation Safety Policies o Staff Dose Monitoring, Staff Pregnancy, Source
Inventory, Calibration of survey meters, Policy for Diagnostic Radiology,
• Staff dose monitoring program o
o Started in 2008
o Full records on file since start date
o Dose constraints set at 0.4 and 0.8 mSv
• Staff Radiation Safety Training o
o
• Quality Control program for diagnostic Radiology o Performed by
Diagnostic Medical Physicists
o QC to European standards
o Cover all diagnostic radiology machines
• Radioactive source inventory and monitoring system o Full inventory of
sources
o Audits carried out
o Leak testing of radioactive sources
• Emergency response via CBRNE (Chemical Biological Radiation Nuclear
Explosives) Teams
o Can respond to both internal and external emergencies
o Details in the Disaster Plan
AHS Instadose Service
The Medical Physics department at AHS manages Instadose service for those personnel who are
involved with ionizing radiation.
This service is operated through a local agency.
When the results are received, they are analyzed to see if there are any values that are above the dose
limits we set at AHS.
Dose Limits
The dose limits set are those given by the ICRP and the same as those in the UAE regulations and
limit the annual dose to 20 mSv for radiation workers.
However at AHS we have set dose constraints to further limit doses. These constraints are set to 0.4
mSv and 0.8 mSv per month, limiting doses to 25% and 50 % of the ICRP dose limits. Personnel who have received doses in excess of 0.4 mSv but below 0.8 mSv will be informed and we
will try and establish the cause of the high dose, corrective action will be taken if possible. Those
personnel who have a reading above 0.8 mSv will have a more in depth investigation as to why they
received this high dose and corrective action will be taken. All these exceptions will be reported and
reviewed by the Radiation Safety Committee.
The Medical Physics department will issue annual reports of results to departments so that they can
be displayed on the notice boards in their departments.
Glossary of Terms
Words which are underlined are cross-references to other Glossary definitions.
Absorbed Dose A dosimetric quantity, measured in grays where one gray is equal to one joule of
energy deposited in one kilogram of tissue. One gray is a very large dose, so in practice milligray
(mGy) and microgray (μGy) are more often used.
Activity Activity is a measure of the rate at which decays occur in a quality of a radionuclide. Can
also be used to represent the quality of a radionuclide. Unit: Becquerel; Symbol: Bq. One Bq
corresponds to the decay of one atomic nucleus per second.
Acute Radiation Syndrome A well defined patterns of events following exposure to a large acute
dose of radiation to the whole body. Clinical signs initially appear similar to allergic responses or
food poisoning, and may required cytogenetic tests of blood samples to identify radiation as a cause.
Adequate Training Tuition leading to competence in radiation protection and appropriate
instruction, including practical experience, in the diagnostic or therapeutic techniques to be used.
ALARA “As Low As Reasonably Achievable”, taking social and economic factors into account, is
the general principle applied to radiation exposures. ALARA has to be adopted in order to comply
with the Ionising Radiation Regulations of 1985 and 1988. This is the level to which radiation
exposure should be limited. Similar in practice to ALARP
ALARP “AS Low as Reasonably Practicable”. This is a term which is used in Law, therefore
ALARP has a different legal interpretation to ALARA . The Ionising Radiation Regulations 1988
state that: “Persons physically directing a medical exposure shall select procedures such as to ensure
a dose of ionizing radiation to the patient as low as reasonably practicable in order to achieve the
required diagnostic or therapeutic purpose.”.
Alpha Particle An Alpha particle is a Helium nucleus; i.e. it consists of two protons and two
neutrons bound together. It has a double positive charge. Its formula is: - HE 2+
They have a range of a
few centimeters in air and can be stopped by the dead other layer of the skin. However, they are
hazardous if taken into the body. For example in alpha particles are breathed into the lungs they can
damage the living cells of the surface of the lungs.
Alternative Imaging Methods These are methods other that the traditional methods which employ
the use if ionizing radiation. Three examples of such methods are Magnetic Resonance Imaging or
MRI, Ultrasound and Thermography. They are believed to have none of the associated risks of
traditional investigative methods which use ionizing radiation.
ARSAC The Administration of Radioactive Substances Advisory Committee (ARSAC) is a
committee whose primary role is to advise Health Ministers on the issue if certificates for the
administration of such substance to persons.
Atom The smallest discrete particle of an element. An atoms consists of nucleus,
which normally contains protons and neutrons, surrounded by electrons. Matter is made up of atoms,
which may be combined into molecules such as DNA, proteins, water etc.
Atomic Mass Unit A convenient unit of mass which is define as being 1/12 of the mass of one atom
of Carbon-12 (the most common isotope of carbon). 1 proton or 1 neutron have a mass
approximately equivalent to 1 Atomic Mass Unit (a.m.u.). 1 a.m. = 1.66 x 10 -27
kg
Atomic Number The number of protons contained in the nucleus of an atom. If an atom has a
neutral charge then the atomic number equals the number of electrons in the atom.
Atrophic A wasting, progressive degeneration with lack of healing of any tissue of the body.
Attenuation There is a major difference between the interaction of charge particle radiation (e.g.
beta radiation) with matter and the interaction of electromagnetic radiation with matter (e.g.
gamma radiation)
Charge particles have a definite range in matter (e.g. beta particles can travel up to 2 mm through
human tissue), whereas it is possible to predict the range of electromagnetic radiation.
A beam of gamma radiation is never completely absorbed when it passes through matter. A certain
fraction of the gamma radiation will be absorbed depending on the thickness of the absorber. For
certain energy and type of radiation it is possible to discover the thickness of material which will
attenuate the beam to half its original value.
Becquerel See Activity
Beta Decay Beta particles are emitted in the process of beta decay. A neutron changes to a proton and
an electron or vice versa.
In the transformation the nucleus loses a negative charge and emits an electron (e)
In the transformation the nucleus loses a positive charge and emits a positive electron (e+
)
Beta Particle Generally, a negatively charged particle, with mass equal on magnitude to an electron
emitted by a radionuclide. A few radionuclides produce positively charged beta particles called
positrons.
Beta particles have a range of up to a few meters in air and can be stopped by a sheet of Perspex or a
thin metal sheet. They will travel about 1-2 mm in human tissue.
BIR British Institute of Radiology.
Blood Tests Certain non-imaging nuclear medicine tests involve taking blood samples. After the
administration of a radiopharmaceutical the activity in the blood can then be used to calculate organ
function, blood flow etc. depending on the choice of radiopharmaceutical and method of
administration. Blood tests nay also be carried out following a radiation incident to determine an
estimate of the dose received.
Calculations It is possible for Medical Physicists to estimate radiation dose to a patient using
physical calculations based on the variables of the investigation e.g. exposure time, current, voltage
and so on, or details of the radiopharmaceutical used.
Catheter A long fine tube. One use of a catheter is that id can be guided through the circulatory
system to gain access to areas that would otherwise require surgery.
Chernobyl In April 1986, reactor number four at Chernobyl nuclear power station in the Ukraine
exploded, resulting in what has been called the “words” worst man-made disaster”. The fire fighters
tacking the resultant blaze were only allowed to stay on the roof for three minutes to clear radioactive
debris. Although they wore protective clothing, many of them died as a result of the radiation
received. In total, more than forty people died in or after the blast and childhood thyroid cancer in
neighboring Belarus has increased 100-fold. Radioactive debris form the explosion was carried
across Europe and was detected in rainwater falling in the UK.
Chromosomes Fiber-like structures in the cell nucleus, which carry the genes.
Clinical Judgment Regardless of what “guidelines” say, doctors must still make their final decision
using their own clinical judgment based upon their training and experience to make the best decision
regarding the case in hand.
Clinical Justification The use of ionizing radiation must always be clinically justified. A doctor
must expect that the outcome of an investigation will affect the course of treatment for a patient. If
the course of treatment will be the same regardless of the outcome of the radiograph then the
investigation is not clinically justified.
Refer to The Royal College of Radiologists’ Booklet: “Making the best use of a Department of
Clinical Radiology, Guidelines for Doctors” and Book 4 for more information on this subject.
Clinically Directing The POPUMET regulations require that every medical exposure should be
carried out under the responsibility of a person who is clinically directing such an exposure in
accordance with accepted diagnostic or therapeutic practice. The person who is clinically directing
the exposure in radiology is the person who decides that the patient should be irradiated. In a hospital
this is commonly the consultant radiologist, radiotherapist or nuclear medicine physician, but nay be
a cardiologist, dentist, orthopedic surgeon, hematologist etc.
Such people are clinically directing (and sometimes physically directing) the exposure and are
required to ensure that the exposure is carried out “in accordance with accepted diagnostic or
therapeutic practice:. See also Physically Directing
Collective Dose The “collective dose” is the total effective dose to a group or population. It is
usually used in terms of a dose from a specific source applied to a specified population e.g. The
Annual Collective Dose from x-ray examinations in the UK. It is measured in man Sieverts.
Compton Effect In this process a photon (e.g. a gamma ray) interacts with a “free” electron of an
atom. The photon transfers some of its energy to the electron, which is ejected from the atom leaving
it ionized. The electron that has been ejected behaves like beta particle and also goes on to cause
further ionization.
The photon now has a reduced energy but is scattered (Compton Scattering) and can go on to:
Undergo further ionizations by Compton interactions or photoelectric interactions, or,
Escape from the tissue – it is scattered photons which are of particular concern in the clinical
environment.
The atom regains stability by capturing another free electrons.
Computed Tomography Computed Tomography (CT) scanning is high dose investigation which
yields detailed cross sectional images. The X-ray emitter and receiver rotate around the patient. The
information is recorded by computer and can be manipulated to show different contrasts levels in
areas of interest. Effectively, the human cross-section has been divided into a grid. Each cell of that
grid has been divided into a grid. Each cell of that grid has been irradiated many times from different
angles. The computer is programmed to analyze the output of each scan in such a way that it can
calculate a “linear attenuation coefficient” for each cell in the grid by solving multiple equations.
This linear attenuation coefficient is then converted to a CT number by comparing it with the linear
attenuation coefficient of water. Finally, the matrix of CT number is displayed as a matrix of shades
of grey. The resulting analyses grid represents the cross section as organ, tissue, bone etc. The
smaller the increment of rotation in the scanner the more detailed the picture, however, with a
proportionally higher dose.
CT scans are commonly used when detailed investigation of the head, chest or abdomen are required,
for example:
Intracranial Problems
Mediastinum and Lung Parenchyma.
Lymphoma (and monitoring response to chemotherapy)
Post-operative complication involving complex masses.
Accurate guidance of drains and biopsies
Trauma.
Congenital Abnormality Varies disorders manifest at birth, including such as neutral tube defects,
cardiac abnormalities and cleft lip/palate conditions.
Constrains See Dose Constraints
Consumer Products Some consumer products contain low activity materials that cause low level
radiation exposure of the public. The most common of these are smoke alarms, radioluminous
timepieces, tritium l and ight sources.
Contrast Media Contrast Media are substances which are administered to a patient to increase the
contrast of organs or vessels when viewed using imaging techniques. The substance can be
of either greater or lower density that the organ or tissue.
Core of Knowledge a person physically directing a medical exposure is expected to have acquired
the following Core of Knowledge, according to the Ionizing Radiation Regulations 1988.
1. Nature of ionizing radiation and its interaction with tissue.
2. Genetic and somatic effects of ionizing radiation and how to assess their risks.
3. The ranges of radiation dose that are given to a patient with a particular procedure, the
principle factors which affect the dose and the methods of measuring such doses.
4. The principles of quality assurance and quality control applied to both equipment and
techniques.
5. The principle of dose limitations and the various ways to reduce patient dose e.g. gonad
shields.
6. The specific requirements of women who are, or may be, pregnant and also of children.
7. If applicable, the precautions necessary for handling sealed and unsealed sources.
8. The organizational arrangements for advice on radiation on radiation protection and how to
deal with a suspected case of overexposure.
9. Statutory responsibilities.
For those clinically directing medical exposure, the following additional knowledge should be
acquired.
10. In respect of the individual diagnostic and therapeutic procedures which the person intends to
use, the clinical value of those procedures in relation to other available techniques used for
the same or similar purposes.
11. The importance of utilizing existing radiological information such as films and/or reports
about a patient.
Decay Product A nuclide or radionuclide produced by radioactive decay. It may be formed directly
from a radionuclide or as a result of successive decays though several radionuclides.
Declared Term of Pregnancy The special dose limits for pregnant staff only apply from the time
that the woman informs her employer that she is pregnant. The period from this time until the time
she leaves work to have her child is described as the Declared Term of Pregnancy.
Dental Radiology Radiology is used in dentistry to assist diagnosis. The average effective dose for a
dental X-ray is about 0.1 mSv. Dental radiology is carried out with a high frequency but it is a low
dose technique- and only accounts for about 1 % of the annual collective dose to the UK population
from diagnostic medical x-rays. Reference: p.94, "Radiation Risks: An Evaluation", Sumner, Wheldon and Watson, 1991
Deterministic Effect A deterministic effect of radiation is when the effect is predictable, generally
with a threshold below which there is no effect. Increasingly severe effects are seen at higher doses.
Deterministic effects include radiation sickness, skin damage (e.g. erythema) and cataracts. See also:
stochastic effect.
Detriment is a measure of the likelihood of ill effects from a radiation dose.
It includes not only the probability (risk) of developing a fatal cancer, but the likely number of years
of life lost. Thus leukemia (relatively high probability, early onset, high death rate) would have a
much higher weight in calculations of detriment than skin cancer (low probability, late onset, low
death rate). In addition, detriment includes terms to take account of the damaging effects on non-fatal
cancers on quality of life, and genetic defects in future generations.
Diagnostic Related with "diagnosis", the process through which a doctor looks at the available
information and symptoms and draws conclusions about a patient's condition.
Diagnostic Radiology Creating images for diagnostic purposes using ionizing radiation. The image
can be created on photographic film or it could be a computer retained image.
Direct The physician who is clinically directing a physical exposure to ionizing radiation is directly
responsible for the clinical justification of that exposure. They need not be administering the dose
themselves. A physician who is physically directing an exposure is responsible for the radiation dose
administered but not necessarily the clinical justification.
DNA Deoxyribonucleic acid (DNA) is a macromolecule in the form of a double helix. Each helix
carries the genetic information needed for cell replication, proteins and nucleic acids.
Dose A shorthand term used for both the amount of radioactivity administered to a patient, measured
in becquerels (Bq) or multiples thereof (MBq, kBq); and radiation dose. Effective dose is often
shortened to just "dose"."
Dose Area Product The dose-area product is a defined as the absorbed dose to air averaged over the
area of the x-ray beam in a plane perpendicular to the beam axis, multiplied by the area of the beam
in the same plane. The dose area product is expressed in Gycm2
.
It is measured by putting a dose area product meter into a collimated X-ray beam.
The Dose Area Product is a particularly useful quantity in Quality Assurance.
Dose Area Product Meter The dose that patients are receiving from x-ray examinations can be
easily measured by using dose-area product meters which incorporate transmission ionization
chamber and are fitted to x-ray sets. The reading on these meters should be recorded in order to help
the department to audit doses.
A measurement is taken of the absorbed dose to air and this is averaged over the area of the x-ray
beam to yield a Dose Area Product value in the units of Gycm2. Reference Dose Area Product values
have been determined for a range of different procedures.
Dose Constraints The dose constraint for a procedure involving ionizing radiation is the maximum
expected radiation dose which may be given to carry the procedure out. This is not a mandatory limit
but a level set locally or nationally, e.g. by the NRPB. If regularly exceeded then a local investigation
should be carried out to ascertain the cause and remedial action taken if necessary.
Dose Equivalent Former term for equivalent dose.
Dose Limitation This is a term used in Radiation Protection and differs slightly in meaning from
Dose Reduction. It is specifically used in the context of dose justification and refers to the
elimination of unnecessary requests for diagnostic radiology i.e. Limit the dose by not performing the
procedure.
Dose Limits Doses received as a result of the use of ionizing radiation should be kept AS Low As
Reasonably Achievable, (ALARA). However, even if the doses have been optimized fully, there is a
maximum dose that a person is permitted to receive in any year. These Dose Limits are set in the
Ionizing Radiations Regulations 1985. They apply both to staff and to members of the public, but not
to patients.
Dose Monitor Dose monitors typically come in two types: Film Badges and TLDs.
The film badge is a simple plastic holder containing a small strip of photographic film. Each month
the film is replaced. If the old film has been exposed to ionizing radiation there will be fogging on
the film. This fogging can be measured and therefore the dose can be assessed for that month. The
radiation worker should wear this holder whenever they are working.
Dose Optimization The process of getting the best possible diagnostic results from a particular
investigation with a specific set of equipment using as Iowa radiation dose as possible.
Dose Reduction A general term used in Radiation Protection which encompasses all methods for
reducing patient dose.
Dose Threshold The dose threshold for a deterministic effect is the minimum dose at which the
effect may be expected to occur. For these effects dose threshold can be considered as the maximum
safe dose.
Dosimeter Measurement or calculation of radiation doses
Doubling Dose The "doubling dose" is the dose that will double the frequency of detectable
mutations occurring spontaneously."
Effective Dose Renamed from: Effective Dose Equivalent when using 1990 ICRP Weighting
Factors. Effective Dose takes into account that on exposure to radiation, there is a varying dose to
each tissue. There is also a different amount of effect depending upon the sensitivity of the tissues
(measured by the Tissue Weighting Factor). The purpose of calculating the effective dose is to find the theoretical dose that would have the same
effect if applied uniformly to the entire body i.e. to carry the same risk. It combines the doses to
the various body organs into a single number which is the equivalent whole-body dose that
would produce the same detriment. Thus we can use it to compare different types of
investigations which use ionizing radiation. Note that it applies only to stochastic effects.
Effective dose is measured in Sieverts.
The equation to calculate this is:
HT = equivalent dose to each organ
WT = tissue weighing factor for the organ
Effective Dose Equivalent Former term for effective dose.
Electromagnetic Radiation Electromagnetic radiation exists in the form of waves and
includes; gamma rays, X-rays, ultraviolet light, visible light, infrared light, microwaves and
radio waves.
Electron A sub-atomic particle with a negative charge and almost no mass (0.0005494 a.m.u.).
Electrons move around the nucleus in an atom.
Electron Capture In this process, an orbital electron is captured by the nucleus and combines with a
proton to form a neutron. If the vacancy that is left is filled by an electron from an outer orbital, the
energy that is lost in this process can be emitted as an X-ray.
electron volt The standard unit for measuring energy is the joule, but the electron volt (eV) is
still widely used as a unit of energy for x-rays and gamma rays. 1 electron-volt (e V) is equal
to the change in energy of 1 electric charge moving through a potential of 1 volt. 1 electron volt is
approximately equal to 1.6 x 10-19
J
Element A chemical substance which contains only one type of atom (i.e. all of the atoms
have the same number of protons).
Embryo Initial development of implanted fertilized ovum. See also: fetus
Endocrinology The study and treatment of the endocrine glands and their secretions.
Entrance Skin Dose Entrance Skin Dose is a measured dose. It is measured using TLD's on
the patient's skin and can then be equated to more useful units of Effective Dose or Organ
Dose using published tables.
Epithelium Tissue forming outer layer of the skin or a body cavity.
Equivalent Dose (measured in Sieverts) To measure the biological effect of a given absorbed dose of
a particular radiation, the LET of the radiation must be taken into account. The effect of the LET is
expressed quantitatively as the radiation weighting _actor and the
equivalent dose is calculated as:
Erythema Reddening of the skin similar to mild sunburn. This would not be observed unless the
living cells beneath the skin had received a dose of several grays.
Exposure Sources These are the sources of radiation that you may be exposed to in day to day
living. For example, medical use of diagnostic radiation, eating seafood which contains radioactive
Polonium, or even wearing a radio luminous watch.
Extravasate If a radionuclide injection is extravasated, this means that the radionuclide has been
injected into the surrounding tissue instead of the vein.
Fatal Cancers Fatal cancers are those from which people die. Cancers of different types have
different fatality rates and this is reflected in calculations of detriment.
Film Reject Analysis This is the evaluation of all films which have been rejected as being un
diagnostic. The reasons for the films being rejected will be evaluated, probably on a weekly basis,
against criteria which may include:
is it overexposed?
is it underexposed?
is the patient in an incorrect position?
has the patient moved?
is there a film processing fault?
Fission Some very heavy nuclei decay by fission, which means the nuclei splits into smaller
fragments. When a nucleus of Uranium 235 absorbs a neutron, it splits into two roughly equal
fragments together with the emission of further neutrons. The neutrons which are emitted can go on
to cause fission in other Uranium 235 nuclei. In enriched Uranium which contains a high proportion
of Uranium 235 nuclei, if this process were to continue then an enormous release of energy would
occur. A controlled release of this energy forms the basis for nuclear power.
Fluoroscopic A fluoroscopic process is one where a fluorescing image is viewed on a screen or
television monitor instead of the image being recorded on film. See also fluoroscopy.
Fluoroscopy The principles of fluoroscopy are basically the same as plain film x-ray. The x-rays in
this case however are used to excite a fluorescent screen which generates a faint image. This image
can then be amplified and viewed on a television monitor.
Fluoroscopy is often used to get a moving picture e.g. a barium meal. The patient swallows the
barium contrast media and this "swallow" is then imaged periodically as it progresses through the
patient. The output can be recorded as several plain films, video, .cine or on more modern machines
as a digital computer retained image.
Fetus Post embryonic development during which human characteristics emerge. See also: embryo
Free Radical A group of atoms containing one or more unpaired electrons. Free radicals are highly
reactive. Ionization of water in the body produces the hydroxyl free radicals which can rapidly
diffuse through cells causing damage to the DNA similar to that of direct radiation damage.
Gamma Camera A gamma camera is used to detect gamma rays that are being emitted by a patient
to whom a dose of radionuclide has been administered. The gamma rays are detected by a single,
large scintillation crystal which is positioned very close to the patient. When a gamma ray hits the
crystal a flash of light is emitted and this is registered on a detector which processes the information
from all scintillations that are occurring and creates an image.
Gamma Ray A discrete quantity of energy, without mass or charge, that is propagated as an
electromagnetic wave. Identical to X-rays apart from the method of production. Gamma rays come
from the nucleus whereas X-rays are due to changes in the energy of electrons.
Genes The hereditary units occupying fixed positions on chromosomes. The genes carry the
information to create the proteins within a cell.
Genetic Effect A genetic effect is a detrimental effect occurring in the descendants of the individual
exposed to a hazard. Caused by damage to the cells of the reproductive system. Compare with a
somatic effect.
Germ Cells involved in the reproductive process.
gray A dosimetric unit, used to measure absorbed dose, expressed as energy deposited per unit mass
of material. The value of 1 gray is 1 joule per kilogram.
The obsolete unit of absorbed dose is the rad, which is equivalent to 10 mGy.
Hematopoietic Blood forming. May be abbreviated to haemopoietic.
Half-life The activity of a sample of radionuclide decreases with time and if it is measured it is found
that:
"The time that is required for the activity of a sample of a radionuclide to decrease
to half its value is a constant which we call the half-life of that substance".
Different radionuclides have different half-lives, varying from fractions of a second to many billions
of years, although those used in medicine tend to have half-lives of a few hours or days.
ICRP The ICRP is the International Commission on Radiological Protection, an international body
which was founded in 1928, to provide general guidance on the use of radiation in all fields including medicine.
Image Intensifier An image intensifier is a device which converts the x-ray image into a light image
which can be viewed by a TV camera and displayed as a real time image on a TV monitor.
Intensifier Screen Intensifier screens are used in conventional radiography to convert the pattern of
X-rays transmitted through the patient into a light pattern which is recorded on X-ray film. Most
conventional X-ray pictures are taken with film sandwiched between a pair of intensifying screens.
These are coated with a material which emits light when it absorbs X-ray photons. This process is
known as fluorescence.
Internal Conversion The nucleus can lose energy as it goes from an unstable state to a more stable
state by emitting some of its energy in the form of a gamma ray which liberates an orbital electron in
the process of internal conversion. This electron is ejected from the atom, leaving the atom with an
electron vacancy in one of its shells. If this electron is replaced by an electron from one of the other
shells then this process will be accompanied by an emission of an X-ray of a characteristic energy.
Interventional Application This is when a surgical operation is carried out using CT, ultrasound,
fluoroscopy or MRI to guide the process. Common usage is to guide catheters or needles typically for
biopsy, angioplasty and drainage purposes. It can also be used for the insertion of stents.
Investigations Imaging Procedures used to obtain clinical knowledge about a patient using Ionising
Radiation or Alternative Imaging Methods.
Ion Electrically charged atom or grouping of atoms.
Ionization The process by which a neutral atom or molecule acquires an electric charge. The
production of ions.
Ionization Chamber An Ionization Chamber is a gas counter that col1ects all the primary electrons
and/or ions created by radiation as an electrical current. The charge collected is equal to the energy
deposited divided by the energy necessary to make an ion pair. Ionisation chambers have a wide
range of applications in radiation dosimetry. They include calibration of
radiotherapy beams, measurement of dose to patients using Dose Area Product meters, monitoring
the output of x-ray sets and measuring the activity of radio pharmaceuticals Reference: Tait, W.H, Radiation Detection, Butterworths, London (1990)
Ionizing Radiation Radiation that produces ionization in matter.
Examples are alpha particles, beta particles, gamma rays, X-rays and neutrons.
Isomeric Transition An atom may be left in an excited state following the emission of a beta
particle. The nucleus may be able to stay in this state for minutes, hours or even days before emitting
a gamma ray
An example is 99m
Tc which is produced when 99
Mo emits a beta particle. 99m
Tc has a half-life of 6 hours
and emits a 140 keV gamma ray.
Isotope Atoms of the same element, which have different masses because of differing numbers of
neutrons in the nucleus. Iso (same) - tope (place) i.e. same place on the periodic table therefore
chemically identical.
IVU The common abbreviation for Intravenous Urogram. The whole of the renal tract can be imaged
using a contrast medium.
joule The modern unit of energy in the metric system.
The joule is a derived unit and its value is 1 newton-metre.
1 joule has the equivalent energy of:
The kinetic energy of an apple falling 1 meter, or,
The energy required to raise the temperature of l cm3
of water by¼ ºC, or,
The energy expended when. 1 ampere is passed through a resistance of 1 ohm for 1 second.
Justifiable This is a keyword in Dose Reduction. There must be a good clinical basis for requesting
any investigation which involves the use of Ionizing Radiation.
kV This is simply the units of kilovolt age. When working with X-rays staff will usually simply talk
about "kV" rather than voltage. The accelerating potential applied to the X-ray tube is referred to as
the kilovoltage or kV. It represents the maximum energy in the X-ray spectrum. This parameter is
sometimes written as kVp, the peak kilovoltage, since the voltage applied to the tube may fluctuate.
The kV determines the penetrating ability of the X-ray beam.
Labeled A labeled compound is one in which a proportion of the atoms are radioactive or to which
radioactive atoms have been chemically bound.
LET (Linear Energy Transfer) The rate at which radiation transfers (loses) energy to a medium,
causing ionization, as it traverses that medium.
Low LET radiation such as beta particles, X-rays and gamma rays cause relatively
sparse ionization.
High LET radiation, such as alpha particles cause a dense track of ionization, and much
more biological damage for the same total energy.
See also: Radiation Weighting Factors.
Leukemia Disease in which there is an excess of white corpuscles in the bone marrow and often in
the spleen and the liver.
Leukocyte A white blood cell. Divided into two main groups:
Granular or polymorphic leukocytes, which include neutrophils, eosinophil’s and basophils.
non granular leukocytes, which include lymphocytes and monocytes.
Local Reference Dose Levels Local values should be established for Reference Dose Levels. These
should be less than the national recommendations. This is to take into account the improvements that
can be made in individual Radiology departments by using high technology equipment and by the
adoption of good practice locally. Alternative way of referring to constraints.
Low Dose Rates Low dose rate means that the person is exposed over a period of time rather than
receiving a large dose all at the same time. A low dose rate is typically considered to be less than 100
mGy per day.
Lymphocyte A white blood cell derived from lymphoid tissues. Sensitive to radiation both at the
stage of dividing parent cells and in the circulating blood. See also: Leukocyte
mA This is the unit of electrical current (milli-ampere). When working with X-rays staff will usually
simply talk about "mA" rather than "current". The electron current in the X-ray tube is measured in
mill amperes or mA. The X-ray mA determines the intensity of the X-ray emission from the tube.
Magnetic Resonance Imaging Formerly known as Nuclear Magnetic Resonance (NMR), Magnetic
Resonance Imaging (MRI) is an imaging method that does not rely on ionising radiation. MRI makes
use of the human body's high content of hydrogen nuclei. Hydrogen has a strong magnetic dipole and
will align when placed in a strong, uniform, magnetic field. When a radiofrequency signal pulse is
applied to these nuclei they alter their axes and then return to their original position. When they
return they emit their own radiofrequency. These emissions can be detected and manipulated to give
a cross-sectional image of the body. Reference: Plaut, Simone. Radiation Protection in the X-ray Department,
Butterworth-Heinemann, Oxford (UK), (1993)
Malignancy The condition of being malignant or resistant to treatment. In the case of a' tumour, the
growth is uncontrollable and there is dissemination.
man sievert A unit to represent the total dose received by a population. This unit is often used in the
calculation of associated costs and detriment. The potential annual collective dose savings for the UK
could be expressed in manSv.
Mass Number Equal to the number of protons added to the number of neutrons in an atom.
Medical Exposure In the Ionising Radiation (Protection of Persons Undergoing Medical
Examination and Treatment) Regulations 1988, "'medical exposure" means exposure of a person to
ionising radiation for a diagnostic or therapeutic purpose.
Medical Physicist A person who has specialised in the application of physics within medicine. One
of the responsibilities of the medical physicist is to become involved with ensuring the safe operation
of equipment such as X-ray imaging equipment.
The Medical Physicist may have the Role of being the RPA within a hospital.
Multifactorial Disorders A broad spread of disorders that are determined by several genetic and
non-genetic factors. The contribution of each factor to the disorder may not be well defined and may
not have been quantified by epidemiological or animal studies.
Natural Background Radiation Everybody is exposed to natural radiation. Examples include:
. Cosmic rays from the sky,
. `Radioactive potassium-40 atoms in our food and drink,
. Gamma rays from soil & building materials
. Alpha and beta particles and some gamma rays from the air that we breathe.
Reference: At-A-Glance Series, "Radiation Doses - Maps and Magnitudes", 2nd Edition, NRPB, 1994
Necrosis Necrosis is the death of tissue within a circumscribed area. This can be caused by ionization
from radiation, particularly beta emitters, in a highly localized area. ,
Neoplastic New growth of tissue in some part of the body, particularly referring to a tumor.
Neutron A sub-atomic particle in the nucleus of an atom, with a neutral charge and an approximate
mass of 1 a.m.u. (1.009613 a.m.u.).
Neutrophil Mature myeloid cell in the circulatory blood with a life span of 4 days.
Non-fatal Cancers These are cancers which are either cured by appropriate treatment or which are
so slow growing that the patient dies of something else in the meantime.
We must consider these types of cancer because of their associated detriment to life.
NRPB The National Radiological Protection Board (NRPB) was created by the Radiological
Protection Act, 1970 to advise the UK Government on matters relating to radiation protection. The
board's function is to provide advice, to conduct research, and, to undertake technical services in the
field of radiation protection in the UK.
Nuclear Medicine This is the area of medicine where radionuclide techniques are applied to the
diagnosis and treatment of human disease.
The largest area of Nuclear Medicine involves diagnostic procedures, such as organ imaging where a
chemical substance is labeled with a radionuclide. The radioactive substance is administered to the
patient and the distribution of the radioactivity over time is then studied using a gamma camera.
These techniques can produce images of organs and can also give information about the functioning
of those organs. Other areas of Nuclear Medicine use radionuclide techniques to measure
concentrations of hormones and other substances in blood, urine and tissues.
A third area of Nuclear Medicine involves the administration of therapeutic doses of radionuclides to
patients.
Nucleus The part of an atom which exists at its core and contains almost all its mass. The nucleus
contains the atom's protons and neutrons.
Nuclide A species of atom characterized by the number of protons and neutrons and in some cases,
by the energy state of the nucleus.
Occupational Exposure This is the exposure to radiation at work. This includes people who work in
the nuclear industry, Ministry of Defense, Research as well as Vets, Medical workers, Dentists etc.
Cancer genes take part in the regulation of growth and differentiation of cells. They may either
promote cell growth, in which case they are known as proto-oncogenes, or they may inhibit cell
growth, when they are known as Tumor Suppressor Anti-oncogenes. Damage to either of these can
affect the risk of development of cancer.
Ophthalmology The study and treatment of eye diseases and refractive errors.
Optimized Optimizing equipment is an important method of Dose Reduction. Optimization is the
iterative process of making the equipment work better i.e. reducing the doses. It is vital that
Radiology, Nuclear Medicine and Radiotherapy departments optimize their equipment as part of their
Quality Assurance programs.
Organ Dose The Radiation Dose absorbed by a particular organ in the body. (Units of sievert (Sv) or
gray (Gy)
Organogenesis The development of organs and organ systems within the fetus starting about the
eighth week after conception.
Otolaryngology The study and treatment of the ear and upper respiratory tract and the diseases
which affect them.
Patient Management Patient management is a broad term used to incorporate all the actions which
you perform on a patient e.g. admit to a ward, x-ray, inject with pharmaceutical etc.
Phantom A phantom is a more or less realistic model of an organ or a part of the human body,
which can be imaged using x-ray or Nuclear Medicine techniques etc. A phantom is
used to assess and optimize the performance of equipment under fairly realistic conditions.
See also: test object
Photoelectric Effect The photoelectric effect is a pure absorption effect that predominates with
low energy photons. The incoming x-ray photon interacts with an inner shell electron,
Which is ejected with considerable energy into the surrounding tissues. The x-ray photon now
disappears having deposited ALL its energy - hence the process is one of pure absorption. An outer
electron now drops down to the inner shell to fill the gap in the inner electron shell and other outer
electrons then follow suit and drop down from one shell to another to fill the next gaps that are
created. This cascade of electrons to new energy levels is accompanied by the emission of excess
energy in the form of light or low energy x-rays.
Photon Photons are another name for "beams" of electromagnetic radiation such as gamma radiation
and X-rays. They are not particles of matter but do have some particle-like qualities. X-ray photons
and gamma photons do not cause ionization directly but some or all of their energy can be transferred
to electrons (beta particles) and these electrons can cause further ionizations.
Physically Directing This means affecting the medical exposure. This is interpreted as selecting the
appropriate factors and pressing the exposure button or injecting a radiopharmaceutica1. Reference: Guidance Notes for the Protection of Persons Against Ionizing Radiation
Arising from Medical and Dental Use, The Royal College of Radiologists, 1988.
Positron Emission Tomography (PET) This is a modern technology, based on the use of a positron
(positive electron) emitting radiopharmaceutical, which can produce images of biochemical changes
in organs like the brain. Each positron is captured by an electron producing two gamma rays
travelling in opposite directions. These are detected and the information fed to a computer which
builds up a slice picture similar to that of a CT.
Practitioner A medical doctor, dentist or other health professional, who is entitled to perform
medical exposures in accordance with national legislation.
Prefixes Prefixes in common use are as follows :
Proton A positively charged sub-atomic particle in the nucleus of an atom, with an approximate
mass of 1 a.m.u. (1.007254 a.m.u.).
Quality Assurance Each Department using ionising radiation should have its own Quality
Assurance programme. Quality Assurance is a management technique that can be carried out to
ensure the production of high quality diagnostic images for the minimum radiation dose to the
patient. This can be done through a combination of methods including:
Fraction Prefix Symbol
10-15
femto f
10-12
pico p
10-9
nano n
10-6
micro u
10-3
milli m
103
kilo k
106
mega M
109
giga G
1012
tera T
1015
peta P
Quality Control program to check equipment, Film Reject Analysis,
Equipment Testing,
Staff Training.
Quality Control The set of operations intended to establish and maintain at optimum levels all
characteristics of performance of a system that can be defined, measured and controlled. In
diagnostic radiology, the x-ray tubes and generators can undergo Quality Control procedures as
can the film/screen combinations and image intensifiers. Film viewers and TV monitors can also
undergo Quality Control procedures to ensure optimum performance.
Radiation The process of emitting energy as waves or particles.
The energy thus radiated.
The term "radiation" is often used as a substitute for "ionizing radiation".
Radiation Dose A measure of the amount of energy deposited in a material by radiation, or the
effects thereof. See absorbed dose, equivalent dose & effective dose.
Radiation Protection Radiation Protection is a simple term used for the process of ensuring that
people are not harmed, directly or indirectly by ionizing radiation. The radiation can be naturally
occurring e.g. Radon, or it can be generated by man e.g. medical diagnostic x-rays. Medical Physics
Departments are involved in Radiation Protection within hospitals and in addition, each department
within a hospital which deals with radiation has a Radiation Protection Supervisor (RPS), whose
advice should be sought in the first instance on radiation protection matters.
Organizations involved in Radiological Protection in the UK include The Health and Safety
Executive, the NRPB, the RCR, Her Majesty's Inspectorate of Pollution and the Administration of
Radioactive Substances Advisory Committee (ARSAC)
Radiation Protection Adviser Any hospital that has employees who are working with ionizing
radiation should employ a person to act as a Radiation Protection Adviser (RP A). Such an
appointment of an RP A is a legal requirement of the Ionizing Radiations Regulations 1985. The RP
A, who is generally an expert physicist, should have been trained in the use of radiation, and should
have a thorough knowledge of the hazards and their control. The RP A should be able to give advice
about matters related to the radiation protection of patients and staff. They should have a thorough
knowledge of the working practices in their establishment and a detailed knowledge of legislation
relating to ionizing radiations. In addition, they should keep up-to-date with the requirements for
radiation use and radiation protection.
The RP A will advise the employer on matters such as :
Identification of Controlled Areas.
appointment of Radiation Protection Supervisors(RPS)s
the significance of exposure.
drawing up of local rules.
Note: The RP A may be an individual i.e. a medical physicist, or an external organization e.g. the
NRPB.
Radiation Protection Supervisor A competent employee should be appointed by an employer as a
Radiation Protection Supervisor (RPS) to ensure compliance with The Ionizing Radiation
Regulations (1985) for work involving ionizing radiation.
Within each department there will be a person designated as the Radiation Protection Supervisor
(RPS). The RPS must have a management role in the area for which he/she is responsible and will
commonly be a Superintendent Radiographer.
They will have varying duties which include:
1) Implementing and ensuring compliance with the local rules.
2) Providing internal advice on radiation protection issues.
3) Ensuring personnel dosimeter procedures are adhered to.
4) Ensuring the appropriate protective clothing is worn.
Radiation Sickness A general term referring to sickness varying from marked fatigue to vomiting
and diarrhea caused by exposure to excessive radiation.
Radiation Weighting Factor The biological effect of 1 grey of a particular radiation is different
depending on its LET. Some types of radiation are more damaging than others and this is expressed
as the radiation weighting factor:
Type and Energy
range
Radiation
Weighting
Factor, WR
Gamma rays & X-
rays, all energies
1
Beta particles, all
energies
1
Neutrons, energy:
< 10 keV 5
10 keV -100 keV 10
>100 keV - 2 MeV 20
> 2MeV - 20 MeV 10
> 20 MeV 5
Protons, energy > 2
MeV
5
Alpha Particles 20
Reference: ICRP (60), 1990 Recommendations of the International Commission on Radiological
Protection, Annals of the ICRP, Volume 21, No. 1-3, Pergamon Press"
Radiation Worker This is a person whose job involves the use of ionizing radiation. These include
workers at Nuclear Power Stations, Medical Physicists, Radiographers, Radiologists and
Radiological Nurses.
Radioactive Decay The spontaneous transformation of a radionuclide. The decrease in the activity
of a radioactive substance.
Radioactivity Any element or substance which spontaneously emits ionizing radiation possesses a
property called radioactivity.
Radiograph This is the "hard copy" result of an imaging procedure involving ionizing radiation e.g.
the photographic film or computer retained image. The term radiograph refers to each single view
taken in a procedure not the whole procedure. Radiographs are normally used for diagnostic purposes.
Radiographer An expert in producing radiographs. Some radiographers operate CT scanners, MRl
scanners or ultrasound scanners. All of these produce film, pictures or digital computer images that
can be used for medical diagnosis.
Radiography The discipline concerned with creating images using ionizing radiation to obtain an
image on photographic film or a computer retained image. Usually these
images are for diagnostic purposes. See also: radiographer, radiograph, radiologist.
Radiological Protection A term frequently used instead of radiation protection.
Radiologist A radiologist is a medical doctor who has specialized in the area of radiology.
Radiologists diagnose diseases from x-rays and scans.
Radiology The process of clinical imaging to allow diagnosis using ionizing radiation e.g. x-ray,
fluoroscopy and radionuclide studies. Radiology departments also use the alternative imaging
modalities of ultrasound and MRI.
Radiology Departments This is the department (usually within a hospital) which performs the
radiological investigations required in day to day healthcare. They are specialists in the use of x-rays,
fluoroscopy, CT etc as well as ultrasound and MRI.
Radionuc1ide An unstable nuclide that emits ionizing radiation. (Combination of protons, neutrons
that make it unstable).
Radiopharmaceutical A particular radionuclide or chemical compound containing a radionuclide, in
a form pure enough to be administered to patients, for the purpose of diagnosis or therapy.
Radiotherapy Radiotherapy is an important use of ionizing radiation. Large doses of radiation,
sufficient to cause cell death, are used to deliberately destroy abnormal cells or tissues. There
are several ways of doing this. Radiation can be administered for example by external beams,
either of x-rays, electrons, neutrons etc. from machines, or beta or gamma rays from
radioactive sources. In some circumstances, internal radiation sources may be used. These
can be small radioactive sources physically placed on or in the abnormal tissue, or
radioactive chemicals that are accumulated by the tissue. This method tends to give less
damage to surrounding normal tissue than with external beams. In general, the doses received
in radiotherapy are much higher than those received in diagnostic procedures involving
ionizing radiation. This CALRAD course will concentrate on the diagnostic uses of ionizing
radiation. Radiotherapy will not be discussed to any great extent.
Radon A naturally occurring gas which is released from the rocks and exists to a different extent
depending on the part of the country in which you live. Certain Radon isotopes are alpha and gamma
emitters. Some of the progeny of Radon are alpha emitters. Alpha radiation is a high LET radiation.
High LET radiation is of particular concern where particles may be inhaled and trapped in the lung or
taken up in the bone. For this reason there are many studies in progress of the hazard to the public
from the alpha particles in radon gas, that are emitted naturally from the ground.
RCR The Royal College of Radiologists, the professional association to which Radiologists belong.
The Royal College of Radiologists have produced a set of Guidelines for Doctors, "Making the best
use of a Department of Clinical Radiology" to help doctors working in hospitals and in primary care
to select the most appropriate imaging investigations for their patients. The Guidelines should also
make for a reduction in radiation dose and better clinical practice.
Reference Dose Reference levels have been established for the radiation doses administered during
an investigation that uses ionizing radiation. If the measured dose is found to exceed the reference
level then there is an indication that some part of the exposure routine was incorrect eg human error
or equipment malfunction. This value is largely used as a dose constraint in Quality Assurance.
Reference Dose-Area Product The Reference Dose-Area Product is a value established as a limit to
X-ray procedures. A table of Reference Dose-Area Products has been established for convenience.
This value is used particularly in Local Quality Assurance. If the Dose-Area Product for an
examination exceeds the reference level it indicates that some part of the exposure routine was
incorrect e.g. human error and equipment malfunction.
See also: Dose-Area Product.
Reference Dose Levels Reference levels have been established for the radiation doses administered
during an investigation which uses ionizing radiation. The levels were set by working out achievable
dose levels for typical examinations for a standard sized patient, taking into account good practice
regarding diagnostic and technical performance. This value is largely used as a constraint in Quality
Assurance. If the measured dose is found to exceed the reference level then there is an indication that
some part of the exposure routine was incorrect e.g. human error or equipment malfunction.
Risk In radiation protection the risk to a person is defined as:
1. the probability of suffering from the effects of radiation-induced cancer, both fatal and
non-fatal;
2. the probability of causing genetic damage to future generations
These risks have been calculated from the measured effects on various populations of exposures to
high levels of radiation, e.g. atomic bomb survivors, uranium miners etc.
Scatter Radiation scatter occurs during attenuation. On impact with matter some of the photons are
scattered out of the beam. The direction of scattered radiation is effectively random depending on the
interaction between matter and photon.
Scintillation This is the process by which ionizing radiation is converted into visible photons.
Screen This is simply another word for "looking". It is commonly used in Fluoroscopy referring to
the imaging during an investigation. In this situation you are "screening" the patient when the X-rays
are on.
Set Simply a term used to refer to the x-ray equipment i.e. an X-ray set consists of all the pieces of
equipment necessary to perform plain film radiography.
sievert This is the unit used to measure both equivalent dose and effective dose. Abbreviated to Sv.
One sievert is a very large dose and in practice millisievert (mSv) and microsievert (μSv) are used
more often. 1 millisievert (mSv) is roughly 50 times the average radiation dose from a single film
chest X-ray, or, the dose received from cosmic radiation in 50 return flights to the South of Spain !!,
or, LESS THAN HALF of the average annual dose from natural background radiation in the UK.
Reference: At-A-Glance Series, "Radiation Doses - Maps and Magnitudes", Second Edition,
NRPB, 1994 and "Medical Radiation", NRPB, 1994
Somatic Effect A detrimental effect occurring in the individual exposed to a hazard. Compare with a
genetic effect.
Stent As mall semi-rigid tube-which can .be placed across strictures to restore or maintain
correct shape. Stents may be plastic and of small diameter but a more modern alternative
is, to use expandable metal stents.
Stochastic Effect A stochastic effect of radiation has no threshold below which there are no effects.
Stochastic effects are random in nature, but the probability of such an effect increases with increasing
radiation dose. However, the severity of the effect does not depend on the dose. The main stochastic
effects are cancers and genetic damage.
See also: deterministic effect.
Surface Counter This is most commonly a gamma counter. It can be used to measure the activity
over the heart, liver, spleen etc. (usually over a period of time) to determine specific body
functionality.
Test Object The performance of an imaging device such as an x-ray machine or a gamma camera
must be checked frequently. This can be done by imaging a test object, commonly a pattern of lead
and plastic, to obtain quantitative or semi-quantitative data on the resolution, contrast etc. of the
imaging equipment, and of its day-to-day consistency. The results will not necessarily show exactly
how well the equipment will perform in the clinical situation.
See also: phantom
Therapeutic The property of offering therapy.
Therapy Therapy means treatment of a disease or disability.
Thermography The use of an infra- red sensitive camera to produce pictures of the temperature of
the skin.
Example include image of the legs to detect areas of severity decreased blood flow, and images of
various parts of the body to detect areas of inflammation etc.
Tissue Weighting Factor Certain types of tissue are more susceptible than others to cancer
induction from radiation and therefore irradiation of these tissues poses a greater risk to the patient.
The risk is expressed as a tissue weighting factor and is used in the calculation of effective dose.
Note: For the purposes of calculation, "Remainder" is made up of the following tissues and organs:
adrenals, brain, upper large intestine, small intestine, kidney, muscle, pancreas, spleen, thymus and
uterus.
Reference:
ICRP (60), 1990 Recommendations of the International Commission on Radiological Protection,
Annals of the ICRP, Volume 21, No. 1-3, Pergamon Press
TLD Abbreviation used for:
1. Thermoluminescent Dosimetry.
2. Thermoluminescent Dosimeter.
Thermoluminescent Dosimetry uses small discs or rods etc. of materials such as Lithium Fluoride
LiF or Calcium Sulphate, CaSO4 which absorb radiation and then release the energy absorbed as
light when they are heated to a high enough temperature.
The amount of light released is proportional to the radiation dose received.
The discs of LiF or other Thermoluminescent materials are known as TLDs.
By placing a TLD on a patient before exposing them to ionising radiation it is possible to measure
the patient's entrance skin dose by analysis of the TLD.
Transepidermal Injury. Formation of papules or raised plaques of thickened skin, leading to
superficial desquamation and various degrees of dermatitis.
Transmission Ionisation Chamber This works on the same principle as the normal ionisation
chamber however, the device is radiotransparent and does not affect the beam intensity. It is typically
found on the output tube of an X-ray set.
Ultrasound In diagnostic imaging, ultrasound is the use of high frequency sound waves to image the
surfaces inside the body. The sound waves penetrate the body but as they pass through interfaces
Tissue or organ Tissue Weighting
Factor..WT
Gonads 0.20
Bone morrow (red) 0.12
Colon 0.12
Lung 0.12
Stomach 0.12
Bladder 0.05
Breast 0.05
Liver 0.05
Oesophagus 0.05
Thyroid 0.05
Skin 0.01
Bone Surface 0.01
Remainder 0.05
WHOLE BODY TOTAL
1.00
between tissues of different densities some of the beam is reflected back from the internal surface.
This reflected beam can be detected and manipulated to create an image of the layers of tissue.
Urine. Tests Certain non-imaging nuclear medicine tests involve taking urine samples. After the
administration of a radiopharmaceutical the measurement of the level of activity in the urine can be
used to calculate organ function depending on the choice of radiopharmaceutical and method of
administration.
Vascular Pertaining to the blood vessels.
Whole Body Counter A whole body counter is a large sensitive radiation detector for. estimating the
total quantity of radionuclide in a patient. Typically it will be composed of four scintillation
detectors.
It is usually located in a heavily shielded room reduce the background radiation.
X-Ray A discrete quantity of energy, without mass or charge, that is propagated as a wave. Can be
propagated by bombarding atoms of tungsten in an X-ray machine with electrons.
X-rays differ from gamma rays only in their origin.
Gamma rays come from the nucleus whereas X-rays are produced as a result of changes in the
energy of electrons in the electron shells. The ejection of an electron from a shell will leave a
vacancy which can be filled by an electron from another shell with an accompanying emission of an
X-ray. In the example above a vacancy has been created in the innermost electron shell of an atom.
X-rays behave in a similar way to gamma rays, but the energy of X-rays means
that they tend to be less penetrating: