basic physics radiation

Chapter 1: Radiation Physics

Introduction

Why do we have this course?

The use of X-ray fluoroscopy has increased dramatically in recent years and is

spreading beyond the radiology department where users traditionally have

extensive fluoroscopy training. The power of fluoroscopy units, especially

portable units, has steadily increased. Thus, there is a higher potential for

excessive radiation exposure to personnel and patients. The FDA has articulated

particular concern about the following procedures (TableI-1):

Table I-1: Procedures of Particular Concern to FDA

Procedures Involving Extended Fluoroscopy Exposures ¤ ¥

Radiofrequency cardiac catheter ablation

Percutaneous transluminal angioplasty (PTCA, PTA)

Vascular embolization

Stent and filter placement

Thrombolytic and fibrinolytic procedures

Percutaneous transhepatic cholangiography

Endoscopic retrograde cholangiopancreatography (ERCP)

Transjugular intrahepatic portosystemic shunt (TIPS)

Percutaneous nephrostomy, biliary drainage, or stone removal

¤ FDA 1994

¥ Note: The risk of adverse radiation effects originating from a medically

necessary procedure is almost always offset by the benefit received by the

patient. However, in order to improve the benefit-risk tradeoff for these

procedures, it is incumbent on the operator to understand radiation effects and

utilize methods to avoid them or reduce their severity.

This course is written as a primer for medical personnel who use fluoroscopy

equipment in the practice of medicine. It covers some basic principles of radiation

physics, biology, and radiation safety in order to provide an understanding of the

optimal utilization of fluoroscopy, while minimizing exposures to the patient,

operators, and their colleagues. This course is a supplement to, and is not a

substitute for, traditional medical education.

Radiation Exposure and Public Health Measures

The greatest single source of man-made radiation exposure to the average

person in the United States comes from medical irradiation. Medical doses range

from a few mrad for a chest X-ray to thousands of rad in the treatment of cancer.

The average U.S. citizen gets an effective dose from diagnostic medical radiation

of about 100 mrad per year (Figure I-1)

Figure I-1: Sources of Radiation Exposure

Studies indicate that this medical radiation exposure can be reduced by

optimizing the use of fluoroscopy (NRCP 1989). These optimizing procedures

are given in Table I-2:

Table I-2: Optimizing Action Ranking for Fluoroscopy

Optimizing Action Potential Dose Reduction Factor

Audio output related to

X-ray machine output1.3

Optimization of Video

Camera system3

Required switching

between High (Boost) and Normal

modes

1.5

Optimizing Operator

Technique2 to 10

Clearly good operator training is a very important means of reducing medical

radiation doses. This program is designed to give a minimal understanding of

radiation use and effects in medicine to assist in optimizing the techniques used.

Basic Radiation Physics

Knowledge of basic radiation physics is necessary for properly understanding

fluoroscopy safety.

Courtesy of Albert Einstein Archives

Radiation

What is radiation?

Radiation: is the transfer of energy in the form of particles or waves.

Energy: the ability to do work (Force·Distance)

X-rays are electromagnetic radiation. Electromagnetic radiation is a form of

pure energy which is carried by waves of photons. Electromagnetic radiation is

also known as light. Visible light, Radio and X-rays are all forms of

electromagnetic radiation which vary in energy and thereby wavelength and

frequency as well (Figure 1-1).

Figure 1-1: Forms of Electromagnetic Radiation

Courtesy of Phil Rauch and Laura Smith, 2000

Ionizing Radiation

X-ray radiation contains more energy than ultraviolet, infrared, radio waves,

microwaves or visible light. X-ray radiation has sufficient energy (>30 eV) to

cause ionizations. An ionization is a process whereby the radiation removes an

outer shell electron from an atom (Figure 1-2).

Figure 1-2: The Ionization Process

Alan Jackson, 2001

Non-ionizing radiation does not contain sufficient energy (30 eV) to cause

ionizations (Figure 1-3). While some non-ionizing radiation can be harmful, the

ionization process is clearly able to cause chemical changes in important

changes to biologically important molecules (e.g. DNA).

Figure 1-3: Non-Ionizing Radiations

Courtesy of Alan Jackson, 2001

X-ray Production

X-rays are produced when high velocity electrons are decelerated (slowed or

stopped) or by a nucleus of an atom especially by high atomic number material,

such as the tungsten target (anode) in a X-ray tube. An electrically heated

filament (cathode) within the X-ray tube generates electrons that are accelerated

from the filament to the tungsten target by the application of a high voltage to the

tube. The energy gained by the electron is equal to the potential difference

(voltage) between the anode and cathode. This electron energy is typically

expressed in kilovolts (kV). The accelerated electron interacts with the target

(anode) nucleus. As the electric field of the electron interacts with nucleus, the

electron releases energy in the form of X-rays. This method of of x-ray

production is called bremsstrahlung or braking radiation (Figure 1-4).

FIgure 1-4: X-ray Production (Bremstrahlung)

Courtesy of the University of Michigan Student Chapter of the Health Physics Society

Since the degree of interaction of the accelerated electron with the target nucleus

can vary, the energy spectrum, or distribution of energy, of the X-rays produced

by the bremsstrahlung process is continuous.

As smaller number of characteristic x-rays are also produced as excited

electrons interact with the electrons of the target atoms. The X-rays produced

from this interaction, with a given orbital electron, have a single specific energy

(discrete) instead of a continuous spectrum. Mammographic x-ray tubes are

designed to maximize characteristic production to optimize breast tissue

imaging. The amount of characteristic X-rays in a fluoroscopy beam is relatively

low.

The lower energy X-rays are absorbed within the X-ray tube. This reduces the

number of lower energy X-rays in the resultant spectrum since the lower energy

X-ray are less penetrating. The beam is considered "harder" when there is more

filtration. Most X-ray manufacturers add filtration, commonly consisting of

aluminum, since lower energy X-rays do not contribute to images and add to

patient dose.

The resulting x-ray spectrum energy (Figure 1-5) is a mixture of the characteristic

and bremsstrahlung radiation, less the primarily low energy X-rays absorbed by

the X-ray tube (and added filtration). The maximum energy of the X-ray

produced is equal to the maximum potential applied across the x-ray tube. This

peak X-ray energy is usually described with the unit kVp (kilovolt peak or kilovolt

potential). The type of target anode, potential (kVp) and added filtration produce

a beam of a given "quality" which implies specific shape of an X-ray spectrum.

Figure 1-5: Simplified X-ray Spectrum

Alan Jackson, 2001

X-ray Machine Parameters

The quantity of electron flow (current) in the X-ray tube is described in units of

milliamperes (mA). The rate of X-ray production is directly proportional to the X-

ray tube current. Higher mA values indicate more electrons are striking the

tungsten target, thereby producing more X-rays. The voltage (kVp) primarily

determines the maximum X-ray energy produced but also influences the number

of X-rays produced. Increasing the kVp attracts more electrons from the filament

increasing the rate of X-ray production. However, this relationship is not directly

proportional but higher kVp setting will result in a substantial increase in the

number of X-rays produced. The total number of X-rays produced at a set kVp

depends directly on the product of the mA and exposure time and is typically

described in terms of mA-s or mAs. Fluoroscopy is usually performed using 2 to

5 mA current at a peak electrical potential of 75 to 125 kVp.

X-ray Production Efficiency and Heat Loading

The production of x-rays is a relatively inefficient process so that only a small

fraction of the energy imparted by the decelerating electrons is converted into X-

rays. The remaining energy is converted to heat. Thus, the production and

dissipation of heat in the X-ray tube is a serious consideration. Thus, most x-ray

machines have rotating anodes to spread out the heat to prevent anode melting.

This is the reason why you can hear an X-ray machine make noise. Most

fluoroscopic x-ray machine anodes are primarily based on tungsten due to

tungsten's high melting point, excellent heat transmission, and high atomic

number. In spite of tungsten's favorable qualities, with sufficiently high usage, X-

ray production is prevented by the system to protect the tube. Substantial

improvements have been recently made in the ability of fluoroscopic X-ray

equipment to remove waste heat and thereby maintain high beam outputs.

Figure 1-6: Heat Production

Courtesy of: Phil Rauch and Laura Smith, 2000

Divergent Nature of X-ray Radiation

Once generated, the X-rays are emitted in all directions in a uniform manner

(isotropically). The lead housing surrounding the X-ray tube limits X-ray

emission through a small opening or port in the X-ray tube. The resulting primary

beam of useful radiation is shaped by additional lead shutters, or collimators, that

can be adjusted to provide different beam shapes or sizes.

Inverse-Square-Law (Radiation intensity with distance)

Since the initial beam travels in straight but divergent directions, geometry in a

three dimensional world dictates that the radiation intensity will decrease with the

inverse square of the distance. Consequently, the number of X-rays traveling

through a unit area decreases with increasing distance. Likewise, radiation level

decreases with increasing distance since exposure is directly proportional to the

number of X-rays interacting in a unit area. The intensity of the radiation is

described by the inverse square law equation:

Where XA is the radiation exposure rate at distance DA compared with the

exposure rate (XB) at some other distance (DB).

This effect is shown graphically in Figure 1-7:

Figure 1-7: Inverse Square Law

Courtesy of Scott Sorenson, 2000

1-Meter Distance: 1,000 X-rays pass through a

unit area. The amount of X-rays per unit area is

1,000.

2-Meter Distance: With increasing distance, the

beam diverges to an area 4 times the original area.

The same 1,000 X-rays are evenly distributed

over the new area (4 times the original). Thus the

amount of X-rays per unit area is 250 or 1/4 the

original. The resulting radiation exposure is 1/4

less.

This relationship indicates that doubling the distance from a radiation source

decreases the radiation level by a factor of four. Conversely, halving the

distance, increases the radiation level by a factor of four. Intelligent application

of inverse square law principles can yield significant reductions in both patient

and operator radiation exposures.

Example 1:

An operator normally stands 1 meter away from the patient during

cineangiography. The exposure rate at this point is 15 mrem/min (this unit will be

explained later) and total cineangiography time is 2 min. What is the reduction

should the operator stand 1.2 meters away?

Solution 1:

The original exposure was 30 mrem (15 mrem/min for 2 min). The new exposure

would be:

A 31% percent reduction in radiation exposure is achieved in this example.

X-rays Interactions with matter

X-rays have several fates as they traverse tissue. These fates fall into 3 main

categories (Figure 1-8):

Figure 1-8: X-ray Interaction-Imaging Considerations


No interaction: X-ray passes completely throughtissue and into the image

recording device. Producing an image

Complete absorption: X-ray energy is completely absorbed by the tissue. This

produces radiation dose to the patient.

Partial absorption with scatter: Scattering involves a partial transfer of energy to

tissue, with the resulting scattered X-ray having less energy and a different

trajectory. This interaction does not provide any useful information (degrades

image quality) and is the primary source of radiation exposure to staff.

X-ray Interaction with Matter

The probability of X-ray interaction is a function of tissue electron density, tissue

thickness, and X-ray energy (kVp). Electron dense material like bone and

contrast dye attenuates more X-rays from the X-ray beam than less dense

material (muscle, fat, air). The differential rate of interaction provides the contrast

that forms the image.

Tissue Electron Density Interaction Effects:

As electron density increases, the interaction with X-rays substantially increases.

Higher atomic number materials have increased electron density. Thus, bone,

which is substantially comprised of calcium, produces more attenuation, than

tissue, which is comprised of carbon, hydrogen and oxygen (all of which have a

lower electron density or atomic number than calcium). Thus, the image of bone

and soft tissue has contrast, or difference, between bone and soft tissue.

The concept of contrast and electron density X-ray interaction can be shown in

Figure 1-9.

Assume 1,000 X-rays strike the following body portions. The number of X-rays

reaching the recording media (film, TV monitor) directly effect the image's

brightness.

Figure 1-9: Electron Density and Image Contrast


In this example, 900 X-rays are capable of penetrating the soft tissue, while only

400 penetrate the bone (Higher electron density compared with soft tissue). The

contrast between the bone and soft tissue is (900-400)/900 = 0.56.

Tissue Thickness

As tissue thickness increases, the probability of X-ray interaction increases.

Thicker body portions remove more X-rays from the useful beam compared to

thinner portions (Figure 1-10). In fluoroscopy, this effect must be compensated

for while panning across variable tissue thickness to provide consistent

information to the image-recording device.

Figure 1-10: X-ray Penetration as a Function of Thickness


Note that on average, only 1 percent of the X-rays reach the image-recording

device (e.g., image intensifier, film), yielding useful information. Thus, 99 percent

of the X-rays generated are either absorbed within the patient (patient radiation

exposure) or are scattered throughout the examination room (staff radiation

exposure).

Energy

Higher kVp X-rays are less likely to interact with tissue and are described as

more "penetrating." Increasing kVp, thereby generating more penetrating

radiation, reduces the relative image contrast (or visible difference) between

dense and less dense tissue. Conversely, less radiation dose results to the

patient since less X-rays are absorbed. Figure 1-11 illustrates this effect. The X-

rays that do not reach the image recording device are either absorbed in the

patient (patient radiation dose) or are scattered throughout the exam room (staff

radiation dose)

Figure 1-11: X-ray Penetration as a Function of Energy


Application of Radiation Physics

How does these principles of physics relate to radiation safety? (Figure 1-12)

Figure 1-12: Square Hole-Round Peg


The fundamental tie between Physics and fluoroscopy Radiation Safety occurs

during the sequence of steps which lead to radiation biological effects. These

steps are deposition of energy (Figure 1-13) and biochemical changes caused by

X-rays (Figure 1-14).

Figure1-13: Deposition of Energy

Alan Jackson, 2001

Figure1-14: Biochemical changes

Alan Jackson, 2001

The biochemical changes produced by ionizing radiation radiations are the

fundamental event leading to radiation damage. The amount of energy absorbed

in a system is the best way to quantify the radiation damage. The amount of

energy absorbed per mass is known as radiation dose.

Description of Radiation Exposure/Units

There is a myriad of terms describing amount of absorbed by a system. This is

often confusing even to those quite familiar with radiation physics. Terms which

the operator should be aware of include those are:

The X-ray machine output is described in terms of Entrance Skin Exposure

(ESE) and is the amount of radiation delivered to the patient's skin at the point of

entry of the X-ray beam into the patient. The unit for ESE are Roentgens (R) (or

C/kg air in SI units). The unit Roentgen is defined in terms of charge (Coulombs)

created by ionizing radiation per unit mass (kg) of air (1 R =2.58 * 10-4 C/kg air).

The radiation exposure can also be measured at other locations and is the

quantity indicated by many radiation detectors such as Geiger-Muller meters.

This unit recognizes Wilhelm Conrad Roentgen (Röntgen), who invented

(discovered) X-rays, and gave this technology to the world without personal profit

(Figure 1-15). For this achievement, he received the Nobel prize in Physics.

Figure 1-15: Wilhelm Conrad Roentgen


The unit Roentgen is only defined for air and can not be used to describe dose to

tissue. Radiation dose is the energy (joules) imparted per unit mass of tissue and

has the US units of rad (radiation absorbed dose). Patient exposures, particularly

in Radiation Oncology are described in units of radiation dose. There is an

international (SI) unit for dose termed the Gray (Gy). The conversion between

the units is: 100 rad = 1 Gy.

The biological effectiveness of radiations vary. The unit rem (radiation

equivalent man, now person) is used to compare dose received by different types

of radiations (e.g. alpha particles) which have a different capacity for causing

harm than X-ray radiation. This unit is properly termed dose equivalent. The

dose equivalent is the product of the dose times a quality factor. Occupational

radiation exposure is described in terms of dose equivalent. There is an

international (SI) unit for dose equivalent termed the Sievert (Sv). The

conversion between the units is: 100 rem = 1 Sv.

Go To Chapter 2: Radiation Biology Chapter 2: Radiation Biology

Picture Courtesy of Michael Cohen, 1987

Biological effects of radiation

Most people know that radiation is potentially harmful to living systems,

unfortunately there are a number of misconceptions about radiation biology

which are perpetuated in popular culture.

Radiation Biology History

http://www.radiologyresearch.org/radiationsafety/rso_fot_chapter_2.htm

1895-Roentgen announces discovery of X-rays

1896-(4 months later) Reports of skin effects in x-ray researchers

1902-First cases of radiation induced skin cancer reported

1906-Pattern for differential radiosensitivity of tissues was discovered.

Relative Radiosensitivity of Tissue

The relative radiosensitivity (sensitivity to radiation exposure) of a variety

of tissue is shown in Figure 2-1 below:

Figure 2-1: Increasing Sensitivity to Radiation

Alan Jackson, 2001 from Seibert, 1996.

By 1906 Bergonie and Tribondeau realized that cells were most sensitive to

radiation when they are:

Rapidly dividing

Undifferentiated

Have a long mitotic future

Author Note: When DNA, which had not been discovered at this time, has no backup (single strand).

Radiation sensitivity

Radiosensitivity is a function of the cell cycle with late S phase being the most

radioresistant and G1, G2, and especially mitosis being more radiosensitive.

Mechanisms of Radiation Injury

Radiation can directly interact with a molecule and damage it directly. Because of

the abundance of water in the body, radiation is more likely to interact with

water. When radiation interacts with water, it produces labile chemical species

(free radicals) such as hydronium (H.) and hydroyxls (.OH). Free radicals can

produce compounds such as hydrogen peroxide (H2O2) which subsequently exert

chemical toxicity. The body has sophisticated protections against this type of

chemical damage. For example, this is why hydrogen peroxide foams when it is

poured on a cut. The hydrogen peroxide is being destroyed by an extremely

rapid enzyme, hydrogen peroxidase.

Nonetheless, while DNA and other repair methods are extremely capable of

protecting the body, some fraction of the damage is not repaired or may be

repaired incorrectly. In either case, if the DNA is damaged, several things can

happen. The most likely is that the damage will be repaired before the end of the

cell’s growth cycle. If not, the cell will probably die. There is some chance that the

cell will survive and behave differently because of the damaged DNA.

Radiation Damage to DNA

Radiation-induced structural changes to DNA can be readily observed (Figure 2-

2).

Figure 2.2: Radiation-Induced DNA Damage

Photomicrograph showing examples of radiation-induced chromosome damage in cancer cells following radiotherapy treatment

(Bushong 1980). Courtesy of Scott Sorenson.

When DNA is damaged, the harm can be magnified by the cellular machinery.

One example of a possible consequence is a cell which loses control over

replication-this mutation is better known as cancer. Ionizing radiation is thought

to initiate (start), but not promote (help grow) mutations.

Types of Radiation Effects

Acute Effects: Short term effects

Very large radiation exposures can kill humans. The lethal dose(LD) for half the

population (50%) within 60 days is termed the LD50/60d. The LD50/60d in humans

from acute, whole body radiation exposure is approximately 400 to 500 rads (4-5

Gy). The temperature elevation in tissue caused by the energy imparted is much

less than 1° C. The severe biological response is due to ionizing nature of X-ray

radiation, causing the removal of electrons, and therby chemical changes in

molecular structures.

Deterministic Radiation Effects

A number of ionizing radiation effects occur at high doses. These all seem to

appear only above a threshold dose. While the threshold may vary from one

person to another, these effects can be eliminated by keeping doses below 100

rad. The severity of these effects increases with increasing dose above the

threshold. These so-called deterministic (non-stochastic) effects are usually

divided into tissue-specific local changes and whole body effects, which lead to

acute radiation syndrome (Table 2-1).

Acute Whole Body Radiation Effects

Table 2-1: Acute Radiation Syndrome

Sorenson, 2000.

Syndrome Symptoms Dose (rad)

Radiation sickness Nausea, vomiting > 100 rad

Hemopoietic

Significant disruption of

ability to produce blood

products)

> 250 rad

LD50/60d

Death in half the

population > 250 - 450 rad

GIFailure of GI tract lining,

loss of fluids, infections> 500 rad

CNS Brain death > 2,000 rad

These whole body (to entire body) doses are very unlikely for patients and staff from fluoroscopy

or any diagnostic radiology study.

Several factors, such as total dose, dose rate, fractionation scheme, volume of

irradiated tissue and radiation sensitivity all affect a given organ’s response to

radiation. Radiation is more effective at causing damage when the dose is higher

and delivered over a short period of time. Fractionating the dose (i.e. spreading

the dose out over time) reduces the total damage since it allows the body time

for repair. Patient exposures are higher than attending staff but they occur over

short periods of time whereas staff exposures are normally low and occur over

several years.

Acute Localized Radiation Effects

The Table 2-2 provides examples of possible radiation effects to skin caused by

typical fluoroscopy exposures. Note that patient and technique factors can

substantially increase exposure rates, significantly reducing the time necessary

for the subsequent effect.

Table 2-2: Dose and Time to Initiate Localized Radiation Effects

[Specific case studies of radiation-induced skin injury are presented in the next section]

Please note these localized effects will not be seen immediately (in the clinic).

These effects take time to develop and the minor effects may not be noticed and

are often attributed to other causes. This effectively results in a lack of warning

for serious effects such as dermal necrosis. This lack of warning has led the

FDA, HFH Radiation Safety Committee, and HFH Hospital Medical Executive

Committee (HMEC) to have concerns about fluoroscopy utilization.

Consequently, fluoroscopy safety training and monitoring of fluoroscopy times

were mandated.

Chronic Radiation Effects

Cataractogenesis

Cataract induction is of special interest to fluoroscopy operators since the lens of

eye often receives the most significant levels of radiation (provided lead aprons

are used). Radiation is known to induce cataracts in humans from single dose of

200 rad. Higher total exposures can be tolerated when accumulated over time.

Personnel exposed to the maximum levels each year in the State of Michigan

should accumulate no more than 150 rem to the lens of the eye over 30 years.

As such, the risk for cataracts is likely to be small. Nonetheless, it is imperative

that individuals who approach the State of Michigan dose limit (1,250 mrem per

quarter) wear leaded eyewear which can reduce the radiation dose to the eye by

85%. Leaded eyewear will be provided, by Henry Ford Health System, to

individuals with high eye doses. Once leaded eyewear is issued, this must be

worn for all tableside X-ray procedures.

Stochastic (Probabilistic) Effects

Since the discovery of radiation by Roentgen, there have been many groups in

which radiation effects have been studied (Bushong 1980) (Table 2-3):

Table 2-3: Groups Studied for Radiation Effects

Scott Sorenson, 2000.

Groups Studied for Health Effects

American Radiologists

Nuclear weapon survivors

Radiation-accident victims

Radiation-accident victims

Marshall Islanders (Atomic bomb fallout)

Residents with high levels of environmental radiation

Uranium miners

Radium watch-dial painters

Radioiodine patients

Ankylosing spondylitis patients (radiation therapy)

Thorotrast patients (radioactive contrast material)

Diagnostic irradiation in-utero

Cyclotron workers

Radiation Induced Cancer

These experiments have repeatedly shown that exposure to large radiation

doses results in an elevated risk of cancer. Thus, radiation is considered a

known human carcinogen. The experimental data suggest a non threshold dose

response relationship (Figure 2-3).

Figure 2-3: Stochastic Radiation Effects


Extrapolation of effects at higher doses using a straight line, predict that very

small radiation doses have corresponding small risk of causing a cancer. This

straight line assumption, called the linear, no threshold, dose response

relationship (LNT), involves the least amount of mathematical assumptions and

is thereby consistent with the ancient principle of scientific philosophy known as

Okam's razor (the simplest explanation which describes a phenomenon is the

best). There are also some reasonable models which predict this

relationship. The slope of this straight line can be used as a risk coefficient to

compare radiation risks with other hazards.

The LNT hypothesis implies that any amount of radiation exposure will increase

an individual's risk of cancer. Thus, all radiation doses should be mimimized or

kept As Low As Reasonably Achievable (ALARA).

Due to statistical considerations, such as the normal incidence of cancer (~30%),

the ineffectiveness of the production of cancer by radiation, stochastic effects

can only be shown at doses much higher than that received by occupational

workers. The effects from lower radiation exposures (such as those encountered

occupationally) are extrapolated from observations made at high doses (Upton

1999). In any case, this linear assumption is expected to provide the most

conservative, or highest, risk estimates. The slope of the line is the risk

coefficient.

Radiation Risk

The cancer risk coefficient derived from the LNT model for radiation exposure is

approximately 4.8 * 10-4 per rem. To put this number into perspective, imagine

that you have two similar groups of 10,000 people; exposed and not exposed.

Each member of the exposed group receive 1 rem 1,000 mrem) of radiation

exposure. The control group does not recieve any additional radiation exposure

beyond that received by natural sources. Since the natural incidence of cancer is

about 30%, the control group would expect about 3000 people to die from

cancer. In comparison, the exposed group would expect that about 3005 people

would die from cancer. Thus, the exposed group should expect about 5

additional cancers from the 1 rem exposure.

One way better understand radiation risks is to compare radiation risks with other

commonly accepted risks (Figures 2-4 and 2-5).

Figure 2-4: One in Million Risks

Alan Jackson, 2001

Figure 2-5: One in Million Risks

Alan Jackson, 2001

Radiation Induced Genetic Damage

Since radiation causes damage to DNA, genetic effects in human populations

have long been suspected. Unrepaired or incorrectly repaired chromosonal

damage can be passed on to subsequent generations. To date, there have been

no studies which show an increase in genetic disorders in human populations.

Nonetheless, animal studies have shown a relationship between radiation

exposure and genetic defects which suggest a linear, no threshold, dose

response relationship (LNT) much like that seen with cancer.

The 7 million mice, "Megamouse" project revealed the following conclusions

(Lam 1992):

Different mutations differ significantly in the rate at which they are produced by

a given dose.

There is a substantial dose rate effect with no threshold for mutation

production.

The male was more radiosensitive than the female. The males carried most of

the radiation induced genetic burden.

The genetic consequences of a radiation dose can be greatly reduced by

extending the time interval between irradiation and conception. Six months to a

year is

recommended.

The amount of radiation required to double the natural and spontaneous

mutation rate is between 20 to 200 rads.

Radiation apparently does not cause unique types of mutations, but simply

increases the mutations rate above their natural rate of occurrence. Controlled

studies of genetic effects are only available from animal models. The risk

coefficient for serious genetic disorders from radiation exposure is approximately

8 * 10-5 per rem (NCRP 116). This is less than the cancer risk coefficient (4.8 *

10-4 per rem). Thus, if you protect against cancer, you are simultaneously

protecting against genetic effects.

Radiation Induced Premature Aging

In animal populations, radiation was correlated with premature aging .

In-utero Radiation Health Effects

Once conception has occurred (mother is pregnant), the unborn child (fetus) can

be harmed by radiation. Certainly, the unborn child can have the same health

problems that an adult might have such as cancer and genetic defects. The Law

of Bergonie and Tribondeau predicts that a fetus would be exquisitely sensitive to

radiation since they are:

1. Rapidly dividing;

2. Undifferentiated; and

3. Have a long mitotic future.

Studies of children exposed to x-rays in-utero support that prediction. Thus,

based on a concern for cancer induction, X-ray examination of pregnant patients

has transformed from a standard health screening study to an extremely rare

study. Nonetheless, some X-rays of pregnant patients, particularly those to

protect the life of the mother, are performed when necessary to protect the life of

the mother typically under the guidance of a Radiologist.

In addition to the health effects which are a concern for an adult, there is also a

serious concern about the possibility of developmental errors (teratogenesis)

which can occur. There are three general prenatal effects which have been

observed:

1. Lethality;

2. Congenital abnormalities at birth; and

3. Delayed effects, not visible at birth, but manifested later in life.

The expression of effects are dependent upon the dose and stage of fetal

development (Figure 2-6):

Figure 2-6: Fetal Developmental Radiation Risks


A human embryo exposed to greater than 250 rads before 2 to 3 weeks of

gestation will likely result in prenatal death (miscarriage). Fortunately, those

infants, who survive to term at these extreme doses generally do not exhibit

congenital abnormalities.

Irradiation of the human fetus between 4 to 11 weeks of gestation may cause

multiple severe abnormalities of many organs. Irradiation during the 11th to 15th

week of gestation may result in mental retardation and microcephaly. After the

20th week, the human fetus is more radioresistant, however, functional defects

may be observed. In addition, a low incidence (one in 2000) of leukemia has

been observed in individuals who received prenatal radiation.

Medically indicated procedures involving radiation are appropriate for pregnant

women (Brent 1999). However, such procedures should be avoided if alternate

techniques are available or measures should be taken to minimize patient/fetal

exposure. Considering legal complications and ethical dilemmas resulting from

non-optimal prenatal radiation exposure, it is strongly suggested that physicians

consult with a Board-Certified Radiologist before performing fluoroscopy on

potentially pregnant patients.

Occupational Dose Limits

One way to control risks is to establish occupational exposure limits. These

limits are designed to eliminate threshold effects and minimize stochastic risks to

make radiation occupations as safe as other safe industries. The current dose

limits for the State of Michigan are shown in Figure 2-7.

Figure 2-7: State of Michigan Dose Limits

Note: The State of Michigan dose limits, originally promulgated in 1972 and based on older

recommendations, do not reflect the most updated information on dose limit recommendations.

The U.S. Nuclear Regulatory Commission allows a lens of eye dose limit of 15 rem per year and

a skin dose limit of 50 rem per year.

Patient Dose Limits

Medical X-ray procedures are performed to directly benefit the patient. Note that

limits have not been established for how much dose a patient may receive. The

regulations properly leave this matter up to the discretion of physicians. The

purpose of this course is to educate physicians about how to properly make that

decision for their patients. When in doubt, contact a Board Certified Radiologist.

Go To Chapter 3: General Fluoroscopy Concepts Chapter 3: Fluoroscopy

System Description and Operation

Modern fluoroscopy imaging systems (Figure 3-1) consist of: the X-ray tube

which produces X-rays; an Image Intensifier (I-I) that captures or stops the X-

rays and converts the X-ray energy into light; a closed-circuit video system which

ultimately producing a "live" image on a monitor. On some systems the light

output can also be distributed to a spot film or cinematography recording

systems, though the X-ray output must be greater for these imaging modalities.

Figure 1-2: Fluoroscopy System Components



Generator Control

The X-ray generator controls the quantity (number) and quality (spectrum of

energy) of the X-rays produced. There are three basic controls to the generator:

kVp - voltage applied accross the X-ray tube.

mA -Current across the X-ray tube.

Time - starting and stopping the exposure.

From a safety perspective, the beam- on- time is the most important control.

Beam-on-Time (Foot Pedal/Switch)

Radiation exposure during fluoroscopy is directly proportional to the length of

time the unit is activated by the foot pedal or switch. Unlike regular X-ray units,

fluoroscopic units do not have an automatic timer to terminate the exposure after

it is activated. Instead, depression of the switch determines the length of the

exposure which ceases only after the switch is released. Thus, cognizance of

beam-on-time is extremely important to fluoroscopy safety.

X-ray tube Current (mA)

The X-ray tube current (mA setting) essentially controls the quantity of X-rays

produced per unit time. If you double the mA, you double the patient and

operator exposure. The higher current mode (High Level Control or "boost"

mode) dramatically increases the number of X-rays produced and thereby

improves image quality. The boost mode is activated in some systems when the

foot switch is firmly depressed (a light push activates the normal, low dose,

mode). An audible alarm will indicate when the high level mode is being used.

HFH policy limits the rate for the boost mode to 20 R/minute (compared with

maximum of 10 R/minute for the normal, Automatic Brigtness Control (ABC)

mode and 5 R/minute for the manual mode). Both the patient and fluoroscopy

operator dose are proportional to the total amount of current used by the

machine. Thus, a light touch on the pedal (educated use of the boost mode) will

minimize both patient and worker doses.

During normal mode fluoroscopy, the average patient Entrance Skin Exposure

(ESE) is approximately 2 R/min. The level of radiation exposure falls off

exponentially with increasing tissue depth due to attenuation and inverse-square

effects. Only approximately 1% of the original radiation beam reaches the I-I for

image generation.

The ESE exposure rate can be as high as 20 R/min under certain conditions

using a high dose rate or "boost" mode if the patient’s skin is close to the X-ray

tube. During cineangiography, ESE may exceed 90 R/min.

Fluoroscopy Timer

Fluoroscopy machines are equipped with a timer and an alarm which sounds at

the end of 5 minutes of fluoroscopy use. This system is designed alert the user

when the usage is becoming significant and provide additional warnings 5

minutes after each reset. Fluoroscopy systems also display the total fluoroscopy

time for a procedure. There are internal requirements for recording fluoroscopy

times discussed

Fluoroscopy Monitoring

The Radiation Safety Committee requires that the total elapsed fluoroscopy time

be recorded for every procedure that exceeds 10 minutes of fluoroscopy. Certain

areas, primarily in the Henry Ford Hospital, are also required to record all

fluoroscopy times. Sheets used to record fluoroscopy times are available from

the Radiation Safety Office.

Imaging Modes

Automatic Brightness Control (ABC)

Modern fluoroscopy machines produce images from an I-I that captures the

radiation exiting the patient. The machine can be operated in either a manual

mode or in an Automatic Brightness Control (ABC) mode (Figure 3-2). When the

ABC mode is selected, the ABC circuitry controls the X-ray intensity measured at

the I-I so that a proper image can be displayed on the monitor.

Figure 3-2: Automatic Brightness Control System

Courtesy of Phil Rauch, 2000

ABC mode was developed to provide a consistent image quality during dynamic

imaging, When using ABC, the I-I output is constantly monitored and machine

factors are then adjusted automatically to bring the brightness to a constant,

proper level for adequate I-I function. Both patient and operator factors influence

the number of X-rays reaching the I-I. The ABC compensates brightness loss

caused by decreased I-I radiation reception by generating more X-rays

(increasing mA) and/or producing more penetrating X-rays (increasing

kVp). Conversely, when the image is too bright, the ABC compensates by

reducing mA and decreasing kVp.

The radiation exposure rate is independent of the patient size, body part imaged

and tissue type when the manual mode is used. However, the image quality and

brightness are greatly affected (often adversely) by these factors when the

operator "pans" across tissues with different thickness and composition. For this

reason, most fluoroscopic examinations are performed using ABC.

Obese patients drive the X-ray machine output up considerably. Thus, obese

patients have the greatest risk of skin injury.

Magnification Modes

Many fluoroscopy systems have one or several magnification modes.

Magnification is achieved by electronically manipulating a smaller radiation I-I

input area over the same I-I output area (Figure 3-3). A reduction in radiation

input subsequently results, lowering image brightness. The ABC system, in turn,

compensates for the lower output brightness by increasing radiation production

and subsequent exposure to patient and staff. Patient entrance skin exposures

can become quite high when small field of views are used.

Figure 3-3: Field of View


Normal Magnification Mode

Under Normal mode, there is little magnification with the whole beam used to

generate a bright image. The "Normal" mode is used in the majority of

fluoroscopy procedures. The radiation output is sufficient to provide images for

guiding most procedures or observing dynamic functions. The typical exposure

rate at the X-ray beam entrance into the patient Entrance Skin Exposure (ESE) is

2 R/min.

Under Mag 1 mode, a smaller beam area is projected to the same I-I output. The

resulting object size is larger, but the image is dimmer due to the less beam

input.

The Food and Drug Administration (FDA) regulates the construction of all

fluoroscopy systems. For routine fluoroscopy applications, the FDA limits the

maximum ESE to 10 R/min. The use of higher radiation rates ("High Level

Control" or "boost" modes) are useful in situations requiring high video image

resolution. ESE of up to 20 R/min is permitted for short duration. Special operator

reminders, such as audible alarms, are activated during "boost" modes.

Figure 3-4 illustrates the effect of changing Field-Of-View, or magnification

modes, on skin entrance exposure (ESE) for a typical fluoroscopy system:

Figure 3-4: Image Intensifier Input Exposure


Cineangiography

Cineangiography (cine) originally involved exposing cinematic film to the I-I

output, providing a permanent record of the imaged sequence. Technological

advances in film-less imaging have eliminated the film for most systems. The

cine mode extracts several separate diagnostic quality images per minute. The

amount of information collected for each of these images is essentially equivalent

to a normal flat plane X-ray image. The X-ray machine output required to

produce a cine movie is much higher than the level needed for normal

fluoroscopy. Consequently, dose rates during cine image collection are usually

10 to 20 times higher than normal fluoroscopy. For this reason, careful use of

cineangiography is required.

Field Size and Collimators

The maximum useful area of the X-ray beam, or field size, is machine specific.

Most fluoroscopy systems allow the operator to reduce the field size through the

use of lead shutters or collimators. Figure 3-5 shows a diagram of an X-ray tube

and collimator system.

Figure 3-5: X-ray tube and Collimator System


Irradiating larger field sizes increases the probability of scatter radiation

production (Figure 3-6). A portion of the increased scatter will enter the I-I,

degrading the resulting image.

Figure 3-6: Benefits of Collimation


Prudent use of collimators can also improve image quality by blocking-out "bright

areas," such as lung or other low density regions, allowing better resolution of

other tissues.

Benefits from using collimation

Limiting beam size by using the collimators provides many benefits:

1. The patient receives less total radiation exposure since less tissue is in

the radiation beam (Figure 3-7).

2. The workers in the area receive less radiation exposure since there is less

radiation available to scatter toward staff.

3. The image is improved since scatter contributes noise to the image.

Figure 3-7: Collimation Technique


Last Image Hold

Newer fluoroscopy units are often equipped with a last-view freeze-frame or

video recording. Use of these modes allows the operator to view an image at

leisure, avoiding unnecessary patient and staff radiation exposure caused by

constant fluoroscopy use.

Beam Quality (kVp)

The tube voltage (kV) controls the maximum energy of electrons produced by the

X-ray tube and the maximum energy of the resultant X-ray spectrum (kilovolt-

peak energy or kVp). Use of high kVp techniques can reduce patient dose but

contrast between differing tissues is also reduced. Experienced operators can

optimize the choice between image quality and patient dose through careful

adjustment. The ABC on most X-ray systems can change the kVp and mA used

to optimize imaging.

Image Display Monitor

The image quality available to the operator is dependent on proper adjustment of

the image monitor. These image monitor settings are adjusted during service

and annual testing. Operator adjustment of the brightness and contrast controls

can degrade image sharpness, contrast and distortion and should be done if

problems occur during use. If this happens, service should be contacted to

correct the problems. In addition, the eye's ability to discern detail on the image

monitor is improved under low light conditions. The need for good lighting for

surgical needs must be balanced with imaging considerations. Therefore, the

monitor settings should be calibrated for the area in which it is being used.

System Quality Control Checks

Quality Control (QC) checks are extremely important to ensure proper

performance of the equipment. Daily testing is required by JCAHO standards and

should be utilized to track system performance and optimize display monitor

settings. A simple test tool (Fig 3-8) can be used to monitor system

performance. This tool should be used to evaluate the X-ray system each day

prior to use and any discrepancies corrected immediately.

Figure 3-8: Quality Control Checks


Operator Exposure Profile

No portion of the operator's body should be in the primary beam during imaging.

Thus, the majority of the radiation dose received by the operator is due to

scattered radiation from the patient. After interacting with the patient, radiation is

scattered more or less uniformly in all directions (Figure 3-9).

Figure 3-9: Collimation Technique


It is important to note that the patient does not uniformly emit this scattered

radiation since some of the scattered radiation is absorbed or reduced in intensity

by passing through the patient. The intensity of scatter decreases with increasing

distance, due to inverse square law effects (see Chapter 1). Consequently,

scatter radiation is highest near its source (i.e. the X-ray beam entry point on the

patient). Because radiation scattered in the forward direction (into the patient) is

subject the most tissue attenuation, radiation levels are significantly lower on the

I-I side than the X-ray tube side.

Highest scatter radiation levels are often where the operator stands. Radiation

levels increase with decreasing distance from the point of X-ray entry (Figure 3-

10). In general, an operator positioned 3 feet from the X-ray beam entrance area

will receive 0.1% of the patient’s ESE. Staff members positioned further away

receive much less exposure due to inverse square law effects. In almost all

cases, the tableside operator will receive the highest occupational radiation

exposure during the fluoroscopic procedure. Tableside fluoroscopy receive

among the highest occupational radiation exposures within the health system.

Figure 3-10: Radiation Level vs. Entry Point


Radiation levels are highest beneath the table (when the X-ray tube is below the

patient) because the patient provides an effective beam stop (Figure 3-11).

Highest levels are directed at the operator's waist (See bar chart on figure).

Figure 3-11: Patient Shielding


The scatter radiation profile tilts with the X-ray tube. Higher exposure to the

operator’s head and eyes (which have low dose limits) results during oblique

angle projections where the X-ray tube is tilted towards the operator (I-I is tilted

away from the operator). Conversely, radiation exposure is decreased when the

X-ray tube is tilted away from the operator (I-I tilted towards the operator) (Figure

3-12). When possible, the operator should work on the I-I side of the table when

oblique angles are being imaged. While it is contrary to your instincts, generally

you should work closer to the image intensifier than the X-ray tube.

Figure 3-12: Tilt Exposure Profile



Effect of rotating X-ray system. Images taken with the I-I away (Figure 3-12)

result in higher radiation exposure to the operator's eyes compared to images

with the I-I towards the operator (Figure 3-13).

Figure 3-13: Tilt Exposure Profile



Image Quality Versus Patient Dose

A basic principle in Radiology is that you collect dose along with image

information. The clearest, least jittery, images produce the highest doses. Thus,

it is very important for clinicians to judiciously use appropriate judgment when

increasing the X-ray beam output and to learn to work with most amount of

(necessary) imaging imperfections as possible which still allow the needed

clinical outcome.

Go To Chapter 4: Case Studies of Radiation Injury

Chapter 4: Case Studies of Radiation Injury


Non-Symptomatic Skin Reactions

Minor skin reactions caused by X-rays can be easily misattributed to other

causes (e.g. sun exposure or rashes). Also, since these skin reactions are

delayed effects, they typically would not be be seen in the clinic. Thus, patients

and caregivers may not be aware of skin changes that can be caused by lengthy

fluoroscopic procedures (Wagner 1999). The following case study is a useful

example:

1. Physical examination one year following coronary angioplasty identified a

1 x 2.5 cm-depigmented area with telangiectasia on the patient’s left

shoulder. Total fluoroscopy time: 34 minutes.

2. One year after PTCA involving 66 minutes of fluoroscopy, a 10-cm

diameter hyperpigmented area with telangiectasia was evident on the

patient’s right shoulder.

The above skin changes were in areas not visible to the patients and were only

identified upon physical examination.

Symptomatic Skin Reactions

The circumstances leading to symptomatic radiation induced changes are varied.

Case reports are grouped according to common factors in order to identify the

reasons for radiation-induced effects.

PA Fluoroscopy

The posteroanterior (PA) orientation of the fluoroscope, when properly configured

with the image intensifier down close to the patient, is probably the least

problematic with regard to Entrance Skin Exposure (ESE) rate. However,

extended fluoroscopy usage has resulted in reports of skin damage. The

following case study, which did not occur at Henry Ford Health System,

illustrates this effect (Shope 1995).

On March 29, 1990, a 40-year-old male underwent coronary angiography,

coronary angioplasty and a second angiography procedure (due to

complications) followed by a coronary artery by-pass graft. Total fluoroscopy time

estimated to be > 120 minutes. Figure 4-1 shows the area of injury six to eight

weeks following the procedures. The injury was described as "turning red about

one month after the procedure and peeling a week later." In mid-May 1990, it had

the appearance of a second-degree burn.

Figure 4-1: 6-8 Weeks Post Procedure

Courtesy of Wagner, 1999

Note the square pattern of the injury.

Figure 4-2 shows the appearance of skin injury approximately 16 to 21 weeks

following the procedures with small ulcerated area present.

Figure 4-2: 16-21 Weeks Post Procedure


Appearance of skin injury approximately 18 to 21 months following procedures,

evidencing tissue necrosis:

Figure 4-3: 18-21 months Weeks Post Procedure


Figure 4-4 shows a close-up of injury area at 18-21 months:

Figure 4-4: 18-21 Months Post Procedure


Two additional reported cases of radiation-induced injury (Wagner 1999):

1. Following a transjugular intrahepatic portosystemic shunt (TIPS)

procedure involving 90 minutes of fluoroscopy, a discharged patient

developed erythema and discoloration on his back. One year after the

TIPS procedure an ulcer developed, which did not heal, and two years

later it was 4-cm in size. A split thickness skin graft from the right buttock

was performed.

2. Following a TIPS procedure lasting 6 hours and 30 minutes (no indication

of total fluoroscopy time), a 16- x 18-cm hyperpigmented area developed

on the patient’s back and progressed over a period of several months into

a central area with ulceration. After 14 months a split thickness skin graft

was performed leaving a depressed scar at the surgical sight.

These case studies indicate that extensive use of fluoroscopy can induce severe

skin damage, even under the most favorable geometries.

Steep Fluoroscopic Angles

When the fluoroscope is oriented at a lateral or an oblique angle, two factors

combine to increase the patient’s ESE rate. The first is that a thicker mass of

body tissue must be penetrated. The second is that the skin of the patient is

closer to the source because of the wider span of anatomy (Wagner

1999). Example cases are given below:

1. A PA oblique angle using a C-arm involved 57 minutes of fluoroscopy.

Twenty-four hours later the patient reported a stabbing pain in his right

thorax. Three days later an erythema developed which evolved into a

superficial ulcer. At two and half months after the procedure the area was

approximately 12-cm x 6.5-cm and described as a brownish pigmented

area with telangiectasia, central infiltration and hyperkeratosis.

2. A PA oblique angle was employed during a catheter ablation procedure

involving 190 minutes of fluoroscopy. A symptomatic discoloration was

noted several days after the procedure on the patient’s left upper back. In

the next few weeks the area had become painful and was draining. At

seven weeks the area was approximately 7- x14-cm in size and described

as a rectangular erythema with ulcers. After treatment, there was a

gradual lessening of tenderness with reepitherlialization, leaving a mottled

slightly depressed plaque.

3. A steep PA oblique angle through the right shoulder was employed

involving 51 minutes of fluoroscopy. Fourteen days after the procedure, an

erythema appeared on the right shoulder that progressed into moist

superficial ulcer with poor healing. This degenerated into a deep muscular

ulcer requiring a myocutaneous skin graft approximately 14 months after

the procedure.

The temporal progressions of these effects are consistent with high levels of

acute exposure to x-ray radiation. The temporal differences in the responses are

due in part to the levels of radiation received, but are also likely due to variations

in radiation sensitivity amongst the patients.

Multiple Procedures

Although intervals between procedures should permit the skin to recover, healing

might not be complete. This may lower the tolerance of the skin for further

procedures (Wagner 1999). Example cases are given below:

1. A patient underwent two PTCA procedures about one year apart. Skin

changes appeared approximately three weeks after the second procedure.

At seven weeks a cutaneous ulcer had developed over the right scapula

and healed without grafting.

2. A patient underwent two unsuccessful cardiac ablations involving

approximately 100 minutes of fluoroscopy in a lateral oblique orientation.

Approximately 12 hours after the second attempt, an

erythema developed in the right axilla. At one month the area was red and

blistering. At two years the area was described as a 10 x 5cm atrophic

indurated plaque with lineal edges, hyper- and hypopigmentation, and

telangiectasia. The patient was described as having difficulty raising her

right

arm.

3. Three PTCAs were performed on the patient, the last two completed on

the same day approximately 6 months after the first procedure. The total

fluoroscopy time was approximately 51 minutes. Erythema was noted

immediately after the last procedure. This progressed from a prolonged

erythema with poor healing into a deep dermal necrosis. The patient

underwent a successful split thickness skin graft two years after the last

procedure.

4. Past treatment of pulmonary tuberculosis often resulted in many patients

undergoing extensive exposure to fluoroscopy. These patients had a

demonstrated high incidence of breast cancer.

Previous procedures can lower the skin’s tolerance for future irradiation. Prior to

commencing any lengthy fluoroscopic procedure, the patient’s medical history

should be reviewed. The skin of the patient should be examined to ascertain if

any skin damage is apparent should the patient have a history of lengthy

fluoroscopic examinations. Direct irradiation of damaged areas should be

avoided when possible.

Positions of arms

Keeping arms out of the x-ray beam during some procedures can be a difficult.

Careful attention must be given to providing the arms with a resting position that

will not restrict circulation but will at the same time maintain the arms in an area

that is outside the radiation field (Archer 2000).

A middle-aged woman had a history of progressively worsening episodes of

arrhythmia. A radiofrequency electrophysiological cardiac catheter ablation was

scheduled to treat the condition. The procedure employed 20 min of beam-on

time for each plane of a bi-plane fluoroscope. Prior to the procedure the

separator or spacer cone was removed so that the fluoroscopic c-arms could be

easily rotated around the patient. The spacer cone is a spacer attached to the

tube housing designed to keep the patient at a reasonable distance from the x-

ray source. This is done specifically to avoid the high skin-dose rates that can be

encountered near the tube port.

The patient’s arms were originally placed at the patient’s side but the right arm

later fell into a lower position directly in front of this x-ray tube. However,

personnel were not aware of this change because sterile covers were draped

over the patient and did not correctly interpret the image (Figure 4-4). The right

humerus was directly in the beam at the port. Because the separator cones were

removed, the arm was only about 20–30 cm from the focal spot. With the soft

tissue and bone of the arm directly in the beam, the automatic brightness control

drove the output to high levels at the surface of the arm. The cumulative dose

probably exceeded 25 Gy (2500 rad). This procedure was not performed at

Henry Ford Health System.

Figure 4-4: Image of Arm resting on X-ray Tube Port

Courtesy of Archer, 2000

The patient was released from the hospital the day after the procedure. At the

time there were no complaints regarding her arm and no indication of erythema.

About three weeks after the procedure, a bright erythema was demonstrated

(Figure 4-5).

Figure 4-5: Three weeks Post Procedure


The condition worsened and at five months a large ulcer the size of the

collimated x-ray port developed.

Figure 4-6: Five Months Post Procedure


The separator or spacer cone ensures that a minimal distance between the X-

ray source and the patient is maintained (inverse square law effects). For some

X-ray machines, the spacer cone is designed to be removable in order to provide

more flexibility in positioning for some special surgical procedures (e.g., portable

C-arms). There is a risk of very high dose rates to the skin surface when it is

removed.

Skin Sensitivity

Some patients may be hypersensitive to radiation due to pre-existing health

conditions (Wagner 1999).

Erythema developed after diagnostic angiography and liver biopsy. Skin necrosis

requiring rib resection evolved in the same patient after a TIPS procedure. The

wound remained open for five years before a successful cover was put in place.

Investigation into the events revealed that the patient suffered from multiple

problems, including Sjøgren’s syndrome and mixed connective tissue disease.

Injuries to personnel

The following are modern-day examples of how improper use of the fluoroscope

can lead to injuries in personnel (Wagner 1999).

1. Hands of physicians have incurred physiologic changes indicative of high

cumulative doses of chronic low-dose-rate irradiation. Brown finger nails

and epidermal degeneration are typical signs. These changes were the

result of years of inserting hands into the x-ray field with the x-ray tube

above the patient.

2. Four cases of radiation-induced cataract have been reported in personnel

from procedures utilizing the x-ray tube above the patient orientation.

Doses accumulated to hands and eyes from frequently using the fluoroscope

with the tube above the patient can be extremely high. Only routine application of

proper radiation management techniques will be effective at avoiding such high

doses.

Go to Chapter 5: Protection Methods

Chapter 5: Reducing Radiation Exposure


External Exposure Protection

X-ray machines do not produce internal radiation exposure like radioactive

materials. There are three basic protection methods for external sources of

radiation: Minimizing exposure time, maximizing distance from the X-ray tube,

and the utilization of shielding.

Minimizing Exposure Time: Reduce "Beam-on-time"

Radiation exposure during fluoroscopy is directly proportional to the length of

time the unit is activated. Reductions can be realized by:

1. Not exposing patient while not viewing the TV image;

2. Pre-planning images. An example would be to ensure correct patient

positioning before imaging to eliminate unnecessary "panning;"

3. Avoiding redundant views;

4. Operator awareness of the 5-minute time notifications.

Fluoroscopy’s real-time imaging capabilities are invaluable for guiding

procedures or observing dynamic functions. However, there is no advantage over

conventional X-ray techniques when viewing static images. Use of Last-Image-

Hold features, when available, allows static images to be viewed without

continuously exposing patient and operator to radiation.

Human eye integration time or recognition time of a fluoroscopy image is

approximately 0.2 seconds. Therefore, short "looks" usually accomplish the same

as a continuous exposure. Prolonged observation will not improve the image

brightness or resolution (Seifert 1996).

Maximize Distance

A small increase in the operator's distance from the patient can significantly

reduce the operator's exposure. Standing one step further away from the patient

can cut the physician's exposure rate by a factor of 4 (AAPM 1998) (Figure 5-1).

You should periodically self-evaluate you personal technique to identify whether

opportunities to increase distance exist.

Figure 5-1: Benefit of Increasing Distance

Courtesy of Sorenson, 2000.

In percutaneous transluminal techniques, using the femoral approach rather than

the brachial approach yields distance benefits to the operator (Figure 5-2).

Figure 5-2: Influence of Technique


Substantial increases in operator distance may be realized through remote

fluoroscopy activation whenever automated contrast injectors are used.

Many procedures require staff to intermittently interact with the patient near the

fluoroscopy system. The operator can reduce staff exposure by delaying

fluoroscopy until these activities are completed and/or by alerting these

personnel when imaging; especially during high dose rate modes like

cineangiography (Figure 5-3).

Figure 5-3: Benefit of Alerting Staff


Room Lighting

Provisions should be made to eliminate extraneous light that can interfere with

the fluoroscopic examination. Room lighting should be dim to enhance

visualization of the image. Excessive light can decrease the ability of the eye to

resolve detail. Measures taken to improve detail often involve increasing

patient/staff exposure.

X-ray Tube Position

Fluoroscopy examinations have the smallest operator exposure when the X-ray

tube is underneath the examination table (Figure 5-3). Whenever possible, the

operator should avoid the X-ray tube side of the table when imaging oblique or

lateral images.

Figure 5-3: Benefit of Under-Table Position


Note: The benefit is exaggerated-some operator dose occurs on the I-I side.

I-I to Patient Air Gap

The operator must be aware of the X-ray tube-to-patient distance. Positions

closer can lead to extremely high patient exposures due to Inverse-Square-Law

effects (case study). Minimizing the air gap between the I-I and the patient

typically ensures that this distance is maintained. Use of the separator or spacer

cone can prevent serious effects. The spacer cone is a spacer attached to the

tube housing designed to keep the patient at a reasonable distance from the x-

ray source. This is done specifically to avoid the high skin-dose rates that can be

encountered near the tube port. Spacer cones protect patients from extremely

high local exposures by making it physically impossible to get too close to the X-

ray source (inverse-square law effects). For some X-ray machines, the spacer

cone is designed to be removable (Figure 5-3) in order to provide more flexibility

in positioning for some special surgical procedures (e.g., portable C-arms). There

is a risk of very high dose rates to the skin surface when it is removed.

Figure 5-3: Removable Spacer Cone

Courtesy of Rauch, 2000

Reduce Air Gaps

Keeping the I-I as close to patient’s surface as possible significantly reduces

patient and operator exposures (Figure 5-4). The I-I will intercept the primary

beam earlier and allow less scatter to operator and staff. In addition, The

Automatic Brightness Control (ABC) system would not need to compensate for

the increased X-ray tube to I-I distance caused by the air gap. The presence of

an air gap will always increase patient/operator radiation exposure and decrease

image quality.

Figure 5-4: Benefit of Reducing the Air Gap (I-I Close to Patient)


Care should be taken whenever the image view angle is changed during the

procedure (e.g, changing from an ANT to a steep LAO). The I-I is often moved

away from the patient while changing X-ray tube position. Large air gaps can

result if the table or I-I height remains unadjusted.

I-I to Patient Distance Example:

After changing views, a 10-cm air gap between I-I and patient is inadvertently

maintained. What is the increase in radiation exposure to a 20-cm thick patient

positioned with the table 30 cm away from the X-ray source, assuming the ABC

compensates by increasing mA only?

Note: mA only adjustments on ABC systems are reasonably common.

Solution:

Assuming the air gap could have been eliminated by moving the I-I closer, and

that the brightness loss follows the inverse square law:

The brightness level with the air gap is only 69% of the zero air gap brightness.

The ABC system compensates for brightness loss by producing 31% more X-

rays. The exposure rate to the patient and staff is subsequently increased by

31%.

Reducing air gaps between patient and I-I also reduces image blur. Blurring of

the image is caused by geometric magnification caused by air gaps. Gaps

between patient and I-I enhance geometric magnification. The objects will appear

larger with increasing gap size. However, note that image edges are more fuzzy

(Figure 5-4). The degree of "fuzziness" will increase with increasing air gap.

Figure 5-4: I-I distance and Image Blur



Minimize Use of Magnification

Use of magnification modes significantly increases radiation exposure to patient,

operator, and staff (See Chapter 3). Magnification modes should be employed

only when the increased resolution of fine detail is necessary.

Collimate the Primary Beam

Collimating the primary beam to view only tissue regions of interest reduces

unnecessary tissue exposure and improves the patient’s overall benefit-to-risk

ratio. Optimal collimation also reduces image noise caused by scatter radiation

originating from outside the region of interest (See Chapter 3). A good rule of

thumb is that fluoroscopy images should not be totally "round" when collimators

are available for use, the collimator edges should always be visible in the image.

Use Alternate Projections

Continuous exposure of the patient with the same projection (point of X-ray

beam entry) can cause very high skin dose to small areas. Thus, if the point of

X-ray beam (projection) entry can be changed, the skin may be spared from the

harmful effects of radiation. While this is an effective protection method, care

must be exercised to utilize this method intelligently since longer beam paths

through the patient can cause higher patient and worker dose.

Steeply angled oblique images (e.g., LAO 50 with 30 cranial tilt) are typically

associated with increased radiation exposure since: X-rays must pass through

more tissue before reaching I-I. ABC compensates for X-ray loss caused by

increased attenuation by generating more X-rays; Steep oblique angles are

typically associated with increased X-ray tube to I-I distances. The ABC

compensates for brightness loss caused by inverse square law effects by

generating more X-rays. Oblique views may bring the X-ray tube closer to the

operator side of the table, increasing radiation

exposure from scatter.

Operator exposure from different projections.

When possible, use alternate views (e.g., ANT, LAO with no tilt) when similar

information can be obtained (Figure 5-5). The physician can reduce personal

exposure by re-locating himself when oblique views are taken. For example,

dose rates can be reduced by a factor of 5 when the physician stands on the I-I

side of the table (versus X-ray tube side) during a lateral projection (AAPM

1998).

Figure 5-5: Physician Exposure for a variety of Projections


Projections with the X-ray tube neutral or tilted-away from the operator are

highlighted blue, while those tilted towards the operator are in red. Note the

decrease seen between the LAO 40 views. The caudal tilt causes the tube to be

more tilted away from the operator.

Optimizing X-ray Tube Voltage

Selection of an adequate kVp value will allow sufficient X-ray penetration while

reducing the patient’s dose rate. In general, the highest kVp should be used

which is consistent with the degree of contrast required (high kVp decreases

image contrast).

Henry Ford Hospital has many resources available (e.g., Staff Radiologists,

Medical Physicists) to assist the operator in optimizing the fluoroscopy image

while minimizing patient exposure.

Use of Radiation Shields

Use of radiation shielding is highly effective in intercepting and reducing

exposure from scattered radiation (Figure 5-6). The operator can realize radiation

exposure reductions of more than 90 percent through the correct use of any of

the following shielding options. Shields are most effective when placed as near to

the radiation scatter source as possible (i.e., close to patient).

Many fluoroscopy systems contain side-table drapes or similar types of lead

shielding. Use of these items can significantly reduce operator exposures. Many

operators have had little difficulty incorporating their use, even during procedures

requiring multiple re-positioning of the system.

Figure 5-6: Benefit of Hanging Shield


Ceiling-mounted lead acrylic face shields should be used whenever these units

are available, especially during cardiac procedures. Correct positioning is

obtained when the operator can view the patient, especially the beam entrance

location, through the shield.

Portable radiation shields can also be employed to reduce exposure. Situations

where these can be used include shielding nearby personnel who remain

stationary during the procedure.

Use of Personal Protective Equipment

Use of leaded garments substantially reduces radiation exposure by protecting

specific body regions. Many fluoroscopy users would exceed regulatory limits

should lead aprons not be worn. Operator and nearby staff (within 2 meters) are

required to wear lead aprons whenever fluoroscopes are operated at Henry Ford

Hospital. Due to the poor material qualities of Leaded garments, proper storage

is essential to protect against damage (Figure 5-6). Whenever leaded apron are

required, they must be supplied and paid for by your employer (Henry Ford

Health System)

Figure 5-6: Properly Stored Leaded Garments



Lead aprons do not stop all the x-rays. Typically at least a 80% reduction in

radiation exposure is obtained by wearing a lead apron (Figure 5-7). It should be

noted that the apron's effectiveness is reduced when more penetrating radiation

is employed (e.g., the ABC boost's kVp for thick patients). Two piece lead apron

systems are recommended for most users since they provide "wrap-around

protection" and distribute weight more evenly on the user. Some aprons contain

an internal frame that distributes some of the weight from the shoulders onto the

hips much like a backpack frame. So called "light" aprons should be scrutinized

to ensure that adequate levels of shielding are provided. State of Michigan law

requires the use of 0.5 mm lead equivalent aprons.

Figure 5-7: Lead Apron Protection Efficiency


Note that higher tube voltages sharply reduces the shielding benefits of lead aprons. Higher tube

voltages will occur when imaging large patients or thick body portions. Also note that light aprons

(0.25 to 0.35 mm Pb) provide less protection compared to the recommended 0.5 mm thickness.

Thyroid shields provide similar levels of protection to the individual’s neck region.

Thyroid shield use is required for operators who use fluoroscopy extensively

during their practice.

Optically clear lead glasses are available that can reduce the operator's eye

exposure by 85-90% (Siefert 1996). However, due to the relatively high threshold

for cataract development, leaded glasses are only recommended for personnel

with very high fluoroscopy work loads (e.g., busy Radiology and Cardiology

Interventionists). Glasses selected should be "wrap-around" in design to protect

the eye lens from side angle exposures. Leaded glasses also provide the

additional benefit of providing splash protection. Progressive style lenses for

bifocal prescriptions are available from a limited number of manufacturers.

The latex leaded gloves provide extremely limited protection. Standard (0.5 mm

lead equivalent) leaded gloves provide useful protection to the user’s hands.

However, trade-offs associated with use of 0.5 mm leaded gloves include loss in

tactile feel, increased encumbrance and sterility. For these reasons, use of

leaded gloves is left to the operator’s discretion. To minimize radiation exposure

to the hands, the operator should:

1. Avoid placing his hands in the primary beam at all times;

2. Place hands only on top of the patient. Hands should never be placed

underneath the patient or table top during imaging;

3. Consider using leaded gloves if hand placement within the X-ray beam is

necessary or positioned nearby for extended periods of time.

Radiation Monitoring-Dosimeter Badges

Unlike many workplace hazards, radiation is imperceptible to human senses.

Therefore, monitoring of personnel exposed to radiation is performed using a

radiation dosimeter or "badge." Monitoring is useful to identify both equipment

problems and opportunities for improving individual technique (ensuring radiation

doses are ALARA). Monitoring also documents the level of occupational

exposure.

The requirements for dosimetry has been determined by the Radiation Safety

Committee for each work area. These specify the types of dosimeters issued as

well as the collection frequency.

Some workers are issued a single whole body badge (black figure icon). This

whole body dosimeter should be worn on the collar outside of any protective

equipment worn (lead aprons). Readings from this position provide an estimate

of the radiation exposure to the eyes. Dose estimates to the individual’s whole

body are made using the appropriate algorithm. Other workers are issued

multiple dosimeters. These are designed to be worn as shown (Figure 5-8):

Figure 5-8: Protective Devices

Lieto and Jackson, 2000.

Ring badge and Sterility

Infection Control has evaluated the use of ring badges in surgical arenas. For

open surgical theaters, ring badges are contraindicated. Catheter procedures

may be performed with ring badges.

Dosimetry Practices

In order to provide an accurate estimate of personal risk, radiation badges are to

be used at all times when working with radiation. It is also important to turn in the

radiation badges on time. The accuracy of the readings depends on the timely

processing of the dosimeter with the corresponding control dosimeters.

Absent dosimeters are taken very seriously by the institution. Reports of which

individuals have failed to properly return dosimeters (who did not report the loss

of the dosimeter to the RSO) are sent to: the Radiation Safety Committee; the

Department chairs; the Hospital Medical Executive Committee; and the Board of

the institution. To avoid this negative attention, turn your dosimeter in on time

and promptly report the loss of a dosimeter to the Radiation Safety Office. A new

dosimeter will be issued at no cost and your good name will be preserved.

The Radiation Safety Officer (RSO) reviews dosimetry records on a monthly

basis. Investigations of any exposure exceeding the established standards are

performed to determine whether corrective action can eliminate or reduce

exposures for all concerned. The circumstances surrounding most cases of

excessive radiation exposures are often readily mitigated.

Radiation reports are provided annually to all monitored personnel employed or

practicing at Henry Ford Hospital. In addition, monthly reporting of radiation

exposure is available for highly exposed fluoroscopy users. Individuals can

access their personal records at any time, and written dose estimates are

provided upon request.

ALARA Philosophy

Regulatory dose limits should be viewed as the maximum tolerable levels. Since

stochastic radiation effects, such as carcinogenesis, can not be ruled-out at low

levels of exposure, it is prudent to minimize radiation exposure whenever

possible. This concept leads to the As-Low-As-Reasonably-Achievable (ALARA)

philosophy.

Simply stated, the ALARA philosophy requires that all reasonable measures to

reduce radiation exposure be taken. Typically, the operator defines what is

reasonable. The principles discussed in this manual are intended to assist the

operator in evaluating what constitutes ALARA for his/her fluoroscopy usage.

The Henry Ford Hospital administration is committed to ensuring that radiation

exposure to its medical staff and employees is kept ALARA. Full attainment of

this goal is not possible without the co-operation of all medical users of radiation

devices.

Henry Ford Hospital Radiation Safety Program

Hospital administration has authorized the Radiation Safety Committee (RSC) to

oversee all uses of radiation. The RSC is composed of physicians, physicists,

and other professionals who have extensive experience dealing with radiation

protection matters. The committee appoints a qualified expert (Medical Health

Physicist) to administer the day-to-day activities of the Radiation Safety Office.

Summary of Fluoroscopy Safety

1. Keep beam ON-time to an absolute minimum!

2. Always use tight collimation!

3. Do not overuse the magnification mode.

4. Keep the image intensifier as close to the patient as possible, and the tube

as far away from the patient as possible.

5. Keep the kVp as high as possible considering the patient dose versus

image quality.

6. Keep tube current (mA) as low as possible.

7. Minimize room lighting to optimize image viewing.

8. Do not overuse the high dose rate.

9. Personnel must wear protective aprons, use shielding, monitor doses and

know how to position themselves and the machines for minimum dose.

10.Change projections angle for long procedures to minimize local skin

doses.

11.Remember that the X-ray output, patient dose, and area scatter levels

increase for larger patients.

End of Manual!

Acknowledgements:

We wish to recognize the significant efforts of Scott Sorenson who gave a

substantial portion of this course material to the Medical Physics world to support

his public health efforts in fluoroscopy. Please also recognize the work of Ralph

Lieto, Phil Rauch and Laura Smith. Any errors in this training module are the sole

responsibility of Alan Jackson and Donald Peck of the HFH Radiation Safety

Office.

Fluoroscopy Operator Course Examination

Select from one of the following exams, but do not repeat any exam you have

tested with previously:

basic physics radiation

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