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TRANSCRIPT
12/20/2012
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Scope of Health & medical physics in 21Ist century
Prof. Dr. Prof. Dr. Muhammad Attique Muhammad Attique Khan ShahidKhan Shahid
Principal Govt. P/G Principal Govt. P/G College Jhang (Pakistan) College Jhang (Pakistan)
Copyrights ReservedGovt. Postgraduate college of science Faisalabad (Pakistan)
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INTRODUCTION:
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The scope of medical physics, introduction to the biological problem, radiation terms and units, statutory responsibilities. This course is intended to give an overview of some of the Medical applications of Physics.Medical physics has changed dramatically since 1895. There was a period of slow evolutionary change during the first 70 years after Roentgen’s discovery of x rays. With the advent of the computer, however, both diagnostic and therapeutic radiology have undergone rapid growth and changes
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Technologic advances such as computed tomography and magnetic resonance imaging in diagnostic imaging and three-dimensional treatment planning systems, stereotactic radiosurgery, and intensity modulated radiation therapy in radiation oncology have resulted in substantial changes in medical physics. These advances have improved diagnostic imaging and radiation therapy while expanding the need for better educated and experienced medical physics staff.
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Ultrasound, Magnetic Resonance, Computed Tomography, Nuclear Medicine, X-rays, Radiation Therapy, are all branches of medical physics where continued research is being conducted by a very large group of dedicated researchers consisting of highly qualified physicists, engineers and radiologists. The field of medical physics as we know it today started with the discovery of x-rays and radioactivity in the 1890's. The first radiograph was taken by the physicist Wilhelm Conrad Roentgen (1845-1923) in his Wurzburg University laboratory in Germany. It was a radiograph of his wife's hand.
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For his thorough scientific investigations of x-rays he received the first physics Nobel prize in 1901. Follow the links at Emory to share in the excitement of those historical months of January and February 1896. Physicists were also pivotal in using radiation as a treatment for cancer. We can be very proud that Canadian physicist, Harold Johns (1915-1998), developed in the late 1940s the first Cobalt Therapy Unit. For his continued dedication and research he was made an Officer of the Order of Canada in 1976
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• The medical profession also honoured Dr Johns by inducting him into the Canadian Medical Hall of Fame in 1998.
• Physicists have contributed positively to the advancement of the diagnostic and therapeutic fields of medicine. They will continue to play a primary role in the development of physical principles to medicine.
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What is Medical Physics?
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• Medical physics is generally speaking the application of physics concepts, theories and methods to medicine. A medical physics department may be based in either a hospital or a university. Clinical medical physicists are often found in Diagnostic and Interventional Radiology, Nuclear Medicine and Radiation Oncology
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• However, areas of specialty are widely varied in scope and breadth e.g., clinical physiology, neurophysiology (Finland), and audiology (Netherlands). In the case of research based university departments, the scope is even wider and may include anything from the study of biomolecular structure to microscopy and nanomedicine.
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Who are Medical Physicists?
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• Medical physicists are health care professionals with specialized training in the medical applications of physics. Their work often involves the use of x-rays, ultrasound, magnetic and electric fields, infra-red and ultraviolet light, heat and lasers in diagnosis and therapy. Most medical physicists work in hospital diagnostic imaging departments, cancer treatment facilities, or hospital-based research establishments. Others work in universities, government, and industry.
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What do Medical Physicists do?
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Most medical physicists work in one
or more of the following areas:
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Clinical service
• The responsibilities of a clinical medical physicist lie predominantly in the areas of radiotherapy and diagnostic imaging. The roles of a medical physicist in radiotherapy include treatment planning and radiotherapy machine design, testing, calibration, and troubleshooting. The roles of a medical physicist in diagnostic imaging include machine purchasing and installation, testing, quality control, and operation
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Radiation safety
• Medical physicists have expertise in radiation safety. Canadian regulations recognize medical physicists who are certified by the Canadian College of Physicists in Medicine as Radiation Safety Officers for medical radioisotope facilities.
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Research and Development
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• Canadian radiotherapy physicists play a central role in such areas as the design and construction of radiotherapy treatment equipment, the use of heat and lasers in cancer treatment, the theory of radiation absorption and dose calculation and in radiobiology. Imaging physicists are continually developing and improving methods to image body structure and function
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• Canadian laboratories are leaders in positron emission tomography, magnetic resonance imaging, ultrasound, x-ray and radionuclide imaging, biomagnetic mapping, among other areas. Excellence in Canadian Medical Physics Research is recognized annually via the awarding of the Sylvia Fedoruk Prize.
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Teaching
• Most medical physicists are affiliated with universities. Many medical physicists teach in graduate and undergraduate medical physics and physics programs. They also teach radiology and radiation oncology residents, medical students, and radiology, radiotherapy, and nuclear medicine technologists.
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Professional status
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• Most Canadian medical physicists belong to the Canadian Organization of Medical Physicists (COMP). COMP promotes the application of physics to medicine through scientific meetings, technical publications, educational programs, and the development of professional standards. COMP is linked to medical physics organization in other countries through the International Organization of Medical Physics.
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• Many Canadian medical physicists are also members of the Canadian College of Physicists in Medicine (CCPM), which was established in 1979 to recognize proven competence in physics as applied to medicine. Candidates with suitable educational background and experience become members of the college by passing written and oral examinations.
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• CCPM certification is becoming widely accepted in Canada and other countries and is often required at senior levels in medical physics. Each year the college supports continued professional education by sponsoring symposia on specialized topics and by providing a travel award for a young member in honor of Harold E. Johns.
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Employment of Medical Physicists in Canada
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• There are approximately 400 medical physicists working in Canada: 75% work in hospitals and hospital-based research establishments, 7% work for government, 8% for industry, and an additional 10% are university faculty who are not hospital-based. The number of medical physics positions has generally increased by about 5-10% per year.
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Medical Physics Training Programs
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• A prospective medical physicist should first have an honors degree in physics. Courses in computing, electronics, and mathematics are advantageous. They may then undertake graduate work in medical physics or another area of physics followed by a one or two year training program in medical physics. Many universities and clinics across Canada provide training programs and also introduce undergraduate students to medical physics through summer employment programs.
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What do Medical Physicists Do?
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• Medical physicists are concerned with three areas of activity: clinical service and consultation, research and development, and teaching. On the average their time is distributed equally among these three areas.
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Clinical Service and Consultation• Many medical physicists are heavily
involved with responsibilities in areas of diagnosis and treatment, often with specific patients. These activities take the form of consultations with physician colleagues. In radiation oncology departments, one important example is the planning of radiation treatments for cancer patients, using either external radiation beams or internal radioactive sources.
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• An indispensable service is the accurate measurement of the radiation output from radiation sources employed in cancer therapy. In the specialty of nuclear medicine, physicists collaborate with physicians in procedures utilizing radionuclide for delineating internal organs and determining important physiological variables, such as metabolic rates and blood flow. Other important services are rendered through investigation of equipment perfor mance, organization of quality control in imaging systems,
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• design of radiation installations, and control of radiation hazards. The medical physicist is called upon to contribute clinical and scientific advice and resources to solve the numerous and diverse physical problems that arise continually in many specialized medical areas.
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Research and Development
• Medical physicists play a vital and often leading role on the medical research team. Their activities cover wide frontiers, including such key areas as cancer, heart disease, and mental illness. In cancer, they work primarily on issues involving radiation, such as the basic mechanisms of biological change after irradiation, the application of new high-energy machines to patient treatment, and the development of new techniques for precise measurement of radiation.
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• Significant computer developments continue in the area of dose calculation for patient treatment and video display of this treatment information. Particle irradiation is an area of active research with promising biological advantages over traditional photon treatment. In heart disease, physicists work on the measurement of blood flow and oxygenation. In mental illness, they work on the recording, correlation, and interpretation of bioelectric potentials.
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• Medical physicists are also concerned with research of general medical significance, including the applications of digital computers in medicine and applications of information theory to diagnostic problems; processing, storing, and retrieving medical images; measuring the amount of radioactivity in the human body and foodstuffs; and studying the anatomical and temporal distribution of radioactive substances in the body.
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• Medical physicists are also involved in the development of new instrumentation and technology for use in diagnostic radiology. These include the use of magnetic and electro-optical storage devices for the manipulation of x-ray images, quantitative analysis of both static and dynamic images using digital computer techniques, radiation methods for the analysis of tissue characteristics and composition, and the exciting new areas of computerized tomography and magnetic resonance imaging for displaying detailed cross-sectional images of the anatomy. Medical physicists are also engaged in research and development on imaging procedures utilizing infrared and ultrasound sources.
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• Typical examples of the various research areas presently under active investigation may be found in scientific journals dedicated to this field. The journal, Medical Physics, is published by the AAPM. In addition, the AAPM holds two national scientific meetings a year, one in the summer and one in the winter. During the winter meeting, the AAPM conducts scientific sessions in joint sponsorship with the Radiological Society of North America. Special summer courses, workshops, and frequent regional meetings are also held by the AAPM.
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Teaching• Often medical physicists have faculty
appointments at universities and colleges, where they help train future medical physicists, resident physicians, medical students, and technologists who operate the various types of equipment used to perform diagnosis and treatment. They also conduct courses in medical physics and aspects of biophysics and radiobiology for a variety of gradu ate and undergraduate students.
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• The Commission on Accreditation of Medical Physics Education Programs, Inc. (CAMPEP), jointly sponsored by the American College of Radiology (ACR), American Association of Physicists in Medicine (AAPM) and the American College of Medical Physics (ACMP), assures high educational standards in the field.
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Mechanisms of energy loss by ionizing
radiation in biological materials: Classical calculation of energy
loss by heavy charged particles, extension to electrons, ranges of charged particles and Bragg curves. Interaction of neutrons with matter. Mechanisms of energy loss by electromagnetic radiation. X-ray production (kilovolt age and Megavoltage). Radiation dosimetry.
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Use of X-rays for diagnosis
• X-ray imaging: X-ray image transducers and image intensifiers; assessment of image quality and the modulation transfer function. Mammography. X-ray computed tomography. Patient dose measurement and typical doses in diagnostic radiology. Radiation Protection.
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Imaging with radioactive tracers:
• Single-photon imaging: optimal tracer properties; photon detection using a gamma camera; acquisition modes. Tomography image reconstruction: data required for tomography; analytical and iterative reconstruction algorithms. Positron-emission tomography (PET): cyclotron production of positron-emitters; positron emission and annihilation; detection of annihilation photon pairs; acquisition modes; image reconstruction and data corrections.
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Imaging with radioactive tracers:
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Diagnostic ultrasound:
• Interaction of ultrasound with tissue; ultrasound transducer and the ultrasound field; A-, M-, B-modes and real-time imaging; common image artifacts; Doppler techniques; safety considerations; clinical examples.
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Diagnostic ultrasound:
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Magnetic resonance imaging and spectroscopy
• Controlling the magnetic nucleus, proton density T1 and T2 measurements, the imaging process, coil design, field strength and safety considerations, MR spectroscopy.
• Combining imaging modalities:
• Techniques for image registration. Combining images from multiple modalities
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Radiotherapy: • Introduction to radiobiology.
Relative biological effectiveness. Choice of radiation for radiotherapy. Medical linear accelerators. Radiotherapy treatment planning with external beams. Use of CT and MR images in treatment planning. Radiation distribution around closed sources, source distributions and dose specification, equipment and clinical applications.
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DIAGNOSTIC MEDICAL PHYSICS
• In 1895, Wilhelm Conrad Roentgen surprised the world with a revolutionary discovery that gave birth to the professions of diagnostic and therapeutic medical physics. Since then, physicists have worked avidly to develop new discoveries to advance the technology of medical imaging and radiation therapy. The first 70 years after Roentgen’s discovery witnessed the development of higher speed imaging systems, electronic amplification devices, scintillation cameras, ultrasonographic (US) devices, advanced high capacity x-ray tubes, and rapid film processors
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• . However, maturation of the computer has accelerated even more and enabled technology such as computed tomography (CT), magnetic resonance (MR) imaging, and sophisticated interventional fluoroscopy.
• Medical physics in the United States was first recognized as a profession with the formation of the American Association of Physicists in Medicine (AAPM) in November 1958, during the annual meeting of the Radiological Society of North America (RSNA) Many well-known medical physicists practicing in the 20th century made notable contributions to diagnostic medical physics
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• In the early days of radiology, equipment was quite primitive with little or no shielding around the x-ray tube and bare metal high-voltage cables strung across the ceiling . Often the physician responsible for the “x-ray laboratory” served as the technologist,service engineer, and medical physicist to ensure that the equipment was functional.
• An x-ray examination room (Mayo Clinic, Rochester, Minn, circa 1925) with bare high-voltage cables (arrowheads) and little shielding of the x-ray tube (arrow).
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• Major changes in the practice of medical physics started in the early 1970s with the introduction of the CT scanner. This author (J.E.G.) recalls being in the equipment exhibit hall shortly after the exhibits opened at the meeting of the RSNA at the Palmer House Hotel (Chicago, Ill) in 1972. The original EMI CT scanner was on display, and I quickly judged it to be something that the radiology community would not embrace because it produced images with checkerboard-sized pixels
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• I wondered why a radiologist would be interested in something that produced images with such poor spatial resolution? Since that time, medical physicists have learned that other image quality parameters, in addition to spatial resolution, are important in diagnostic imaging. (a) Original EMI CT head scanner (Mayo Clinic, Rochester, Minn, circa 1973) and (b) an 80 × 80-matrix head CT image obtained with it.
• CT made dramatic changes, first in neuroradiology and then in body imaging. It eliminated pneumoencephalography, performed in the dreaded “chair” in which a patient was positioned and, after a portion of the cerebrospinal fluid was removed and replaced with air, rotated around in various positions.
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• . The first (and, fortunately, last) pneumoencephalographic system that I (J.E.G.) evaluated had exceedingly low-contrast images, primarily due to an excessive amount of off-focus radiation and no means of reducing this unwanted radiation. With the x-ray imaging systems available today, off-focus radiation is addressed by means of better x-ray tube design and lead apertures that eliminate most of this problem. In fact, most medical physicists today do not attempt to quantify off-focus radiation.
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• Since the early 1970s, notable technologic changes in imaging have occurred on a rather frequent basis This has caused dramatic changes in the actual practice of diagnostic medical physics, especially because the medical physicist must be up to date with the technology and understand how it functions from both the technologic and clinical perspectives. Furthermore, each time a new modality is introduced, new techniques must be developed for acceptance testing and quality control of the modality to ensure the optimum use of radiation, whether ionizing or nonionizing, and the maximum quality of images. In addition, information from each of the new modalities must be incorporated into the radiology residency programs and into the physics portion of the board examinations.
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• The application of intensifying screens to mammography was a major change in diagnostic imaging. The original use of industrial x-ray film resulted in low-contrast images compared with those produced today. In addition, the radiation exposures were much higher than those used today (eg, 0.1 Gy [10-rad entrance dose] with industrial x-ray film versus 0.01 Gy [1-rad entrance dose] with screen-film systems available today).
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• The first mammographic unit with other than a tungsten target was introduced while industrial x-ray film was being used. The CGR Senographe (GE Medical Systems, Milwaukee, Wis), introduced in 1965, was the first dedicated mammography unit, and its molybdenum anode and filter had many of the essential elements found in modern equipment.
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• One of the major changes in the practice of diagnostic medical physics was the introduction by the American College of Radiology (ACR) of their Mammography Accreditation Program in 1990 which, by means of metamorphosis, became the core of the Mammography Quality Standards Act (MQSA). This program has mandated medical physics support for all mammographic imaging facilities throughout the United States. The results clearly indicate dramatic improvements in mammographic imaging, with improved image quality and optimized radiation doses.
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• The first publications about quality control in diagnostic imaging were published starting in 1968. Before this, the term “quality control” was virtually unheard of in diagnostic radiology. The requirements by the ACR Mammography Accreditation Program and the MQSA program formally introduced quality control into diagnostic radiology.
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• In the past, most staff in radiology departments were not aware of the exposures required for specific x-ray projections. The Joint Commission on the Accreditation of Healthcare Organizations attempted to address this lack of awareness by requiring the posting of radiation exposure levels for typical x-ray examinations. The levels were posted in most departments, but, unfortunately, national benchmark data were seldom used to determine if the departmental exposures were reasonable
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• . The AAPM has established reference values, similar to investigational levels, with which radiation exposure levels in individual departments can be compared (AAPM, written communication, 1999). The concept of reference values was introduced by the International Commission on Radiological Protection in 1991 with further information and recommendations in 1996. If the exposures used for examinations exceed the reference values, then the medical physicist must investigate the reason for the higher exposure levels. If, after investigation, the radiologists and medical physicist agree that the higher levels are warranted, then the higher exposures are justified and can be used.
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• It should be stressed that the reference values are not to be considered as limits on exposures for examinations. The adoption of reference values has resulted in a major change in the way medical physicists will evaluate radiation exposures in the future. More attention will be focused on patient exposures and a concerted effort will be required to ensure that radiation exposures are optimized in all medical imaging departments.
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• The Internet has resulted in many changes in our lives, and these include the ability for medical physicists to interchange information with their colleagues in the United States and throughout the world. The MEDPHYS Listserv is a good example of the rapid interchange of information among professionals to help both the professionals and their patients. More than 2,200 individuals throughout the world subscribe to the listserver and exchange information relevant to medical physics every day, typically with 10–15 or more messages each working day.
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• . It is not uncommon for a medical physicist in the United States to ask a question and receive answers from colleagues in Europe, Australia, South Africa, or any of the 30 or more countries represented on the mailing list. In addition, the Commission on Medical Physics of the ACR, under the leadership of Don Tolbert, PhD, has started using the listserver as a means of communicating with medical physicists who are members of the ACR. The AAPM, under the leadership of Charles Kelsey, PhD, has developed a system that allows medical physicists to obtain continuing education credits from the World Wide Web
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• This is particularly important in view of the increasing need for medical physicists to obtain continuing education credits to maintain their knowledge of rapidly changing technologies and meet requirements for accreditation programs.
• Other changes in diagnostic medical physics include improvements in ionization chambers and dosimeter systems, as well in the movement from film for personnel dosimetry to thermoluminescent dosimeters and now to devices that make use of optically stimulated luminescence
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• Film was difficult to calibrate and was subject to improper handling. Thermoluminescent dosimeters were a major improvement over film, but they did not provide a permanent record. Optically stimulated luminescence devices offer the advantages of thermoluminescent dosimeters and also provide a permanent record that can be reevaluated if questions arise regarding the original measurements.
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• Ionization chambers and dosimeter systems were difficult to use, and many chambers were handmade by physicists for specific purposes. Use of dosimetric systems available today, as well as digitization of information at the chamber, makes the measurement of radiation exposures encountered in diagnostic radiology relatively easy. For example, it is difficult, if not impossible, to saturate the 6-cm3 chambers available today at the high dose rates encountered in diagnostic radiology owing to the design (a cylindric chamber with the anode and cathode a few millimeters apart)
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• Likewise, it is much easier today than it was 10–20 years ago to make accurate measurements of scattered radiation with large-volume chambers (≥180 cm3) with digitization near the chamber, because this eliminates the problems of induced currents in the chamber cables.
• The passing of some of our standard tools in medical physics must surely be mourned. Devices such as the Ardran and Crookes cassette (Nuclear Associates, Carle Place, NY) (for measuring kilovoltage output from an x-ray tube) and the ever-faithful slide rule are just two that come to mind. Today, many medical physics graduate students have neither seen nor used either of these devices—and some are unaware of their prior existence
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• Many are also unaware of how those blue images on a white paper background (xerographic images) were produced or of the prior rise (and fall) of thermography (a thermal surface map of the breast) for breast imaging.
• What other technologies have come and gone that our younger colleagues have not had the opportunity to experience? There are many, some of which our more experienced colleagues may not wish to recall. The following name just a few: dark adaptation by radiologists before fluoroscopy either by sitting in a dark room or wearing red goggles for a minimum of 15 minutes so the dark fluoroscopic images could be seen on the nonintensified screen; 8-inch floppy disks, nine-track tapes
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• and immediate paper prints (Polaroid; Cambridge, Mass) for the storage of CT images; video hard-copy cameras that produced images on film but not consistently and that required almost continuous calibrations; acquisition of CT images requiring 3 minutes or more per section; acquisition of more than one CT section at a time (early CT scanners acquired data for two or four sections at a time—a feature being promoted today as a step forward in fast CT imaging!); rectilinear scanners for imaging in nuclear medicine; and bistable US systems.
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Radiation protection
• Radiation protection has advanced substantially since 1929 when radiologists did not wear a lead apron during fluoroscopy and used kidskin driving gloves to protect the hands . Since 1976, x-ray room shielding has been applied on the basis of National Council on Radiation Protection and Measurements (NCRP) publication 49. This document is being revised by a joint task group formed by the AAPM and the NCRP, which is important for two reasons.
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• Not only will this new method be completely different from that used in the past, the recommendations produced by two of our professional organizations working together will, no doubt, be better than those that either group could produce on their own. In this same light, we must not forget the long and symbiotic relationship between the AAPM and the RSNA, including their cooperation in providing a forum for medical physics research papers, refresher courses, and scientific exhibits during the annual RSNA meeting. Such cooperation benefits our profession, medical physicists, radiologists, and technologists, as well as the entire medical imaging community.
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Diagnostic radiography
• Diagnostic radiography involves the use of both ionising radiation and non-ionising radiation to create images for medical diagnoses. The predominant test is still the X-ray (the word X-ray is often used for both the test and the actual film or digital image). X-rays are the second most commonly used medical tests, after laboratory tests
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• application is known as diagnostic radiography. Since the body is made up of various substances with differing densities, X-rays can be used to reveal the internal structure of the body on film by highlighting these differences using attenuation, or the absorption of X-ray photons by the denser substances (like calcium-rich bones). Medical diagnostic radiography is undertaken by a specially trained professional called a diagnostic radiographer in the UK, or a radiologic technologist in the USA.
• There are several sub-specialities:
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application is known as diagnostic radiography.
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Projection radiography
• The creation of images by exposing an object to X-rays or other high-energy forms of electromagnetic radiation and capturing the resulting remnant beam (or "shadow") as a latent image is known as "projection radiography." The "shadow" may be converted to light using a fluorescent screen, which is then captured on photographic film, it may be captured by a phosphor screen to be "read" later by a laser (CR), or it may directly activate a matrix of solid-state detectors (DR—similar to a very large version of a CCD in a digital camera). Bone and some organs (such as lungs) especially lend themselves to projection radiography
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Projection radiography
• It is a relatively low-cost investigation with a high diagnostic yield.
• Projection radiography uses X-rays in different amounts and strengths depending on what body part is being imaged:
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• Hard tissues such as bone require a relatively high energy photon source, and typically a tungsten anode is used with a high voltage (50-150 kVp) on a 3-phase or high-frequency machine to generate braking radiation. Bony tissue and metals are denser than the surrounding tissue, and thus by absorbing more of the X-ray photons they prevent the film from getting exposed as much. Wherever dense tissue absorbs or stops the X-rays, the resulting X-ray film is unexposed, and appears translucent blue, whereas the black parts of the film represent lower-density tissues such as fat, skin, and internal organs,
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which could not stop the X-rays. This is usually used to see bony fractures, foreign objects (such as ingested coins), and used for finding bony pathology such as osteoarthritis, infection (osteomyelitis), cancer (osteosarcoma), as well as growth studies (leg length, achondroplasia, scoliosis, etc.).
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• Soft tissues are seen with the same machine as for hard tissues, but a "softer" or less-penetrating X-ray beam is used. Tissues commonly imaged include the lungs and heart shadow in a chest X-ray, the air pattern of the bowel in abdominal X-rays, the soft tissues of the neck, the orbits by a skull X-ray before an MRI to check for radiopaque foreign bodies (especially metal), and of course the soft tissue shadows in X-rays of bony injuries are
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Dental radiography Dental radiography uses a
small radiation dose with high penetration to view teeth, which are relatively dense. A dentist may examine a painful tooth and gum using X-ray equipment. The machines used are typically single-phase pulsating DC, the oldest and simplest sort. Dental technicians or the dentist may run these machines—radiologic technologists are not required by law to be present.
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• Mammography is an X-ray examination of breasts and other soft tissues. This has been used mostly on women to screen for breast cancer, but is also used to view male breasts, and used in conjunction with a radiologist or a surgeon to localise suspicious tissues before a biopsy or a lumpectomy. Breast implants designed to enlarge the breasts reduce the viewing ability of mammography, and require more time for imaging as more views need to be taken.
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• . This is because the material used in the implant is very dense compared to breast tissue, and looks white (clear) on the film. The radiation used for mammography tends to be softer (has a lower photon energy) than that used for the harder tissues. Often a tube with a molybdenum anode is used with about 30 000 volts (30 kV), giving a range of X-ray energies of about 15-30 keV. Many of these photons are "characteristic radiation" of a specific energy determined by the atomic structure of the target material (Mo-K radiation)
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• atomic structure of the target material (Mo-K radiation).
• Other modalities are used in radiography when traditional projection X-ray cannot image what doctors want to see. Below are other modalities included within radiography; they are only summaries and more specific information can be viewed by going to their individual pages:
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• Fluoroscopy (angiography, gastro-intestinal fluroscopy)
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X-ray image intensifier and Contrast medium
• Fluoroscopy is a term invented by Thomas Edison during his early X-ray studies. The name refers to the fluorescence he saw while looking at a glowing plate bombarded with X-rays.
• This is a technique that provides moving projection radiographs of lower quality. Fluoroscopy is mainly performed to view movement (of tissue or a contrast agent), or to guide a medical intervention, such as angioplasty, pacemaker insertion, or joint repair/replacement. The latter are often carried out in the operating theatre, using a portable fluoroscopy machine called a C-arm. It can move around the surgery table and make digital images for the surgeon.
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• Angiography is the use of fluoroscopy to view the cardiovascular system. An iodine-based contrast is injected into the bloodstream and watched as it travels around. Since liquid blood and the vessels are not very dense, a contrast with high density (like the large iodine atoms) is used to view the vessels under X-ray. Angiography is used to find aneurysms, leaks, blockages (thromboses), new vessel growth, and placement of catheters and stents. Balloon angioplasty is often done with angiography.
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Double contrast technique
• Fluoroscopy can be used to examine the digestive system using a substance which is opaque to X-rays, (usually barium sulfate or gastrografin), which is introduced into the digestive system either by swallowing or as an enema. This is normally as part of a double contrast technique, using positive and negative contrast. Barium sulfate coats the walls of the digestive tract (positive contrast), which allows the shape of the digestive tract to be outlined as white or clear on an X-ray
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Double contrast technique
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• Air may then be introduced (negative contrast), which looks black on the film. The barium meal is an example of a contrast agent swallowed to examine the upper digestive tract. Note that while soluble barium compounds are very toxic, the insoluble barium sulfate is non-toxic because its low solubility prevents the body from absorbing it.
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A number of substances have been used as positive contrast agents: silver, bismuth, caesium, thorium, tin, zirconium, tantalum, tungsten and lanthanide compounds have been used as contrast agents. The use of thoria (thorium dioxide) as an agent was rapidly stopped as thorium causes liver cancer.
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• Most modern injected radiographic positive contrast media are iodine-based. Patients who suffer from allergy to shellfish may be allergic to iodine, and should consult their physician regarding pre-medication to lessen risk of allergic reaction. Iodinated contrast comes in two forms: ionic and non-ionic compounds. Non-ionic contrast is significantly more expensive than ionic (approximately three to five times the cost), however, non-ionic contrast tends to be safer for the patient
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• causing fewer allergic reactions and uncomfortable side effects such as hot sensations or flushing. Most imaging centers now use non-ionic contrast exclusively, finding that the benefits to patients outweigh the expense.
• Negative radiographic contrast agents are air and carbon dioxide (CO2). The latter is easily absorbed by the body and causes less spasm. It can also be injected into the blood, where air absolutely cannot.
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Dual energy X-ray absorptiometry
• DEXA, or bone densitometry, is used primarily for osteoporosis tests. It is not projection radiography, as the X-rays are emitted in 2 narrow beams that are scanned across the patient, 90 degrees from each other. Usually the hip (head of the femur), lower back (lumbar spine) or heel (calcaneum) are imaged, and the bone density (amount of calcium) is determined and given a number (a T-score).
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• ). It is not used for bone imaging, as the image quality is not good enough to make an accurate diagnostic image for fractures, inflammation etc. It can also be used to measure total body fat, though this isn't common. The radiation dose received from DEXA scans is very low, much lower than projection radiography examinations.
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Computed tomography
• Computed tomography or CT scan (previously known as CAT scan, the "A" standing for "axial") uses a high amount of ionizing radiation (in the form of X-rays) in conjunction with a computer to create images of both soft and hard tissues. These images look as though the patient was sliced like bread (thus, "tomography"-- "tomo" means "slice"). The machine looks similar to an MRI machine to many patients, but is not related.
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• The exams are generally short, most lasting only as long as a breath-hold. Contrast agents are often used, depending on the tissues needing to be seen. Radiographers perform these examinations, sometimes in conjunction with a radiologist (for instance, when a radiologist performs a CT-guided biopsy).
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Radiation Therapy• More than half of all
people with cancer are treated with radiation therapy, a type of cancer treatment that is used to shrink tumors and stop the growth of cancer cells. Keep reading to get the facts on radiation therapy, including what it is, what to expect, and how to cope with side effects
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What Is Radiation Therapy?
• Cancer is a disease that causes cells to grow abnormally and out of control. In radiation therapy, high-energy X-rays are directed at a person's body to kill cancer cells and keep them from growing and multiplying.
• Most people have been exposed to radiation in the form of an X-ray — most likely at a dentist's office. And just like the X-rays given in the dentist's office, radiation therapy is painless. But unlike a typical X-ray, the radiation isn't used just to create a picture of a tooth or broken bone. Radiation therapy delivers higher doses of radiation so that the radiation will kill cancer cells and shrink tumors.
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• While it's killing the cancer, radiation therapy also can damage normal cells. The good news is that normal cells are more likely to recover from the effects of radiation. Doctors take precautions to protect a person's healthy cells when they're giving radiation treatments.
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How Is Radiation Given?
• Doctors can give people with cancer radiation therapy as the only form of treatment. Or they may use a combination of radiation therapy and chemotherapy (a treatment that uses medications or chemicals to destroy cancer cells) to fight the cancer. Other people with cancer may have surgery to remove tumors or cancer cells first and then have radiation therapy. Each person's situation and treatment is different. A person who has cancer will see an oncologist (pronounced: on-kah-luh-jist), a doctor who specializes in cancer treatment.
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Radiation oncologist • A radiation oncologist is a
doctor whose specialty is using radiation to treat cancer. The radiation oncologist will work with other health care professionals to decide on the type and dose of radiation therapy that will best treat a person's cancer.
• Radiation therapy can be given two ways — externally,
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• Internal radiation therapy is very rare in teens — it's usually adults who get this form of treatment.
• With external radiation therapy,
• doctors use a large machine and special equipment that aims specific amounts of radiation directly at the cancer.
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THERAPEUTIC MEDICAL PHYSICS
• The employment of physicists in radiation therapy dates back to soon after x-rays were first used for treatment of diseases in the late 1890s and early 1900s Physicists were needed because the early x-ray machines required constant nurturing to keep them running reliably and with some consistency in dose delivery. Many of the early developments in dose specification and measurement were made by physicists, culminating in the establishment of the first unit of “dose,” the roentgen, in 1928. During this same period, a number of hospitals began to employ physicists to deal with the handling and dosimetry associated with radium and radon brachytherapy.
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• Two pioneers in the United States whose names come to mind readily in this context were Giaoacchino Failla, DSc, and Edith Quimby, DSc, at the Memorial Hospital in New York City
• The next several decades of advances in radiation therapy were primarily concerned with development of treatment machines capable of higher and higher energies, Physicists pioneered the introduction into radiation therapy of the Van de Graaf generator in the 1930s, the betatron in the 1940s and the linear accelerator and the cobalt 60 unit in the 1950s. All of these machines required considerable support by medical physicists. Of special concern in these early days was the unreliability of these treatment machines.
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• Many of the early linear accelerators were not operational more often than they were operational, and some never made it to the treatment of their first patients. Even 60Co units were not immune to major problems. For example, it was not uncommon for the 60Co source to become fixed in the open position. This would mean that the technicians would have to rush into the room to remove the patient from the couch while we physicists manually cranked the source back into the off position. One of the major difficulties we faced in these early years of megavoltage radiation therapy was that the service engineers we had available to correct these problems frequently had little or no radiation therapy experience.
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• The servicemen for diagnostic x-ray machines worked on radiation therapy machines in their spare time. Even though they were usually capable of diagnosing many of the problems by referring to the schematics provided with the machine, actual repair of the problem was often impossible because it was not uncommon to find that the circuitry in the machine did not match that in the schematic.
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• Donald Kerst, PhD, (left) and Gail Adams, PhD, work on the first betatron (University of Illinois College of Medicine, Urbana, Ill, circa 1971) to be used for radiation therapy. Later, Dr Adams became the first President of the AAPM, the first Chairman of the American College of Medical Physics, and the first Editor of Medical Physics.
• These problems were common during the early days of modern radiation therapy. We faced a new challenge every day.
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• Almost all the equipment we physicists used was primitive, if we had any at all. We calibrated our machines with Victoreen R-meters that we charged by means of friction. Our first attempts at computerized treatment planning in the 1950s and 1960s often entailed use of the mainframe computer at the hospital during off-peak hours, such as overnight. Calculation of only a single dose distribution typically took the entire night. The first commercial treatment planning computers were the RAD 8 and the Artronix PC-12 (Fig 4), with 8- and 12-kbytes of memory, respectively ).
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These computers were slow and quite unreliable, often needing a “kick-start” in the morning. To save time, we frequently resorted to hand calculations of isodose curves.
• The Artronix PC-12 treatment-planning computer: rho-theta transducer (A), tapedeck (B), keyboard (C), hard-copy unit (D), storage scope (E), and digital plotter (F).
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• One of our many “delights” was the first generation of isodose plotters, most of which failed to meet specifications, if they could be made to work at all.
• So what has happened in the past 30 years to make things better today? A lot! Treatment machines are now far more reliable, deliver multiple high-energy x-ray and electron beams, and are available with computerized control of almost all parameters. With the aid of very fast three-dimensional treatment planning computers and three-dimensional imaging, we can now make dose distributions conform to the position and shape of the tumor far more accurately than ever before
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• Some of the techniques developed by radiation therapy physicists to improve treatments include intensity modulated radiation therapy, stereotactic radiosurgery, electronic portal imaging, high-dose-rate brachytherapy, US-guided prostate brachytherapy, fast neutron and proton radiation therapy, three-dimensional planning, and CT simulation. We now have numerous protocols for consistency in treatment delivery, calibration, and quality assurance. Dosimetric equipment is now far more sophisticated and includes various solid state dosimeters and reliable beam and film scanners
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• We now have regional calibration laboratories to calibrate our ionization chambers and our brachytherapy source calibrators.
• Without question, these advances have improved radiation therapy, but have they enhanced the job of the radiation therapy physicist? They have certainly made the job easier, but they have also made it more routine. I can well remember when every day presented a new challenge. Nothing was routine. It is better now, but it is probably not as interesting, at least from my (C.G.O.) perspective
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• EDUCATION, TRAINING, AND BOARD CERTIFICATION OF MEDICAL PHYSICISTS
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• Learning how to become a medical physicist is much more organized today than it used to be. Before the 1970s, the most common way to enter the field was on-the-job training with little or no specialized coursework after completion of a graduate degree in physics or a physical science. Alternatively, one might have been fortunate enough to attend one of the four formal medical physics educational programs in North America: Memorial Hospital in New York, NY; the M.D. Anderson Hospital in Houston, Tex; the University of Wisconsin in Madison; or the Princess Margaret Hospital in Toronto, Ontario, Canada. Unfortunately, these were far too few programs to serve all of North America, so on-the-job training had to be sufficient for the vast majority of physicists.
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• Gradually, however, throughout the 1970s and 1980s, graduate medical physics programs began to be established and, in the middle 1980s, the AAPM formed a commission to accredit such educational programs, to be later called the Commission on Accreditation of Medical Physics Educational Programs (CAMPEP). CAMPEP sets the standards for good graduate programs and, to date, 10 graduate programs have achieved accreditation in North America. Another type of training program, the Clinical Physics Residency, has recently begun to emerge and be eligible for CAMPEP accreditation. This is a program similar in concept to residency programs for physician specialists.
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• The intent is for students to first complete a master of science or doctor of philosophy program in medical physics, in which they obtain all their didactic training, and then progress to a residency for 1–2 years to gain clinical expertise before board certification and independent clinical practice. This is a major step forward in formalization of the entire educational experience, but it can only succeed if sufficient funding is available to support these residencies.
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• A major problem with all these efforts to formalize medical physics education is the lack of a legal requirement to practice for any accredited formal specialized education. Consequently, less than 20% of all graduate medical physics programs in North America are accredited). No doubt some of these nonaccredited programs could meet the standards required by CAMPEP, but many might not. Until the profession mandates graduation from an accredited program to practice medical physics, this regrettable situation will continue
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• A somewhat analogous situation exists with board certification. Currently, medical physics can be practiced without certification, although peer pressure and, in a few instances, state licensure may gradually correct this situation. Formal board certification began in 1949 when the American Board of Radiology (ABR) appointed three medical physicists to act as examiners, and the first five radiology physicists successfully completed the examination . Since then, about 1,500 such examinees have become ABR Diplomates . During the 1980s, the petition of the AAPM to become a sponsor of the ABR was denied;
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• During the 1980s, the petition of the AAPM to become a sponsor of the ABR was denied; in response, a second board for the examination of medical physicists, the American Board of Medical Physics, was established by the American College of Medical Physics in 1987 . This new board, directed entirely by medical physicists, began to offer certification in 1990. To date, about 550 medical physicists have been certified by the American Board of Medical Physics. In the meantime, the ABR has accepted the AAPM as sponsors, and the AAPM became full sponsors of the ABR with three trustees in 1994. Recently, there have been movements on behalf of the AAPM and the American College of Medical Physics to try to unify these two boards
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THE JOURNAL MEDICAL PHYSICS
• In 1974, the AAPM formed its scientific journal, Medical Physics. Before this, the only journal of medical physics was Physics in Medicine and Biology, published by the Hospital Physicists’ Association in the United Kingdom. Now, a quarter of a century later, Medical Physics has become an established international journal for medical physics
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• , with a monthly circulation of more than 8,000 readers and more than 300 new scientific articles published annually, more than 30% of which originate outside North America.
• In conclusion, it is clear that medical physics has changed dramatically and rapidly since the late 1800s, as have diagnostic imaging and therapeutic radiology. Most important, medical physics continues to change today, with the rate of change accelerating with time.
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Role of international medical physics organizations
• Existing international organizations involved in medical physics-related activities can be divided into two categories: governmental (IAEA, WHO) and non-governmental (IOMP, EFOMP, AFOMP, etc). Many efforts have been carried out by these organizations, particularly in developing countries, with the goal of improving the level of clinical physics support
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• These organizations have a noble role, although, in the author’s opinion, some approaches to assistance and training provided are not appropriately performed. To be effective, these organizations must be flexible and bring with them realistic training methods and technical support programs. On the other hand, many organizations benefit with tax advantages and circulating monetary resources, which include donations to developing countries. Even though this is not necessarily a drawback, it is important to identify additional motives for such organizations. Therefore, host countries should adopt the assistance that will best suit their own objectives. Acquiring donated equipment can be effective if it is carefully evaluated.
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• Many donating parties do so for tax deduction purposes in their home countries and also to clear space occupied by unemployed equipment. Therefore donated equipment should only be accepted if it meets institutional needs. The IOMP programs for donation of used equipment and establishment of national medical physics libraries in developing countries are good examples of successful collaborative projects.
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• The volunteers in charge of these projects, who are sacrificing their time, deserve to be congratulated for their efforts.
• The main concerns raised about IAEA/WHO policies are that cooperation is conceived only with governmental organizations in member countries. The bottom line is that the decision-makers in some developing countries have limited knowledge about medical physics and lack the deep understanding of current international standards with respect to the requirements for establishing comprehensive cancer care and diagnostic imaging facilities with advanced physics support.
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• For instance, it has been reported in many cases that some projects sponsored by the Agency are not appropriately managed. Those governments should be encouraged to consult the national medical physics societies and to seek their assistance. Due to lack of support by decision-makers, as well as often haphazard assistance programs that do not meet either short- or long-term objectives, many programs have been unsuccessful. Successful collaboration programs require the full support of decision-makers as well as national medical physics associations, in conjunction with appropriate planning.
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Medical physics in developing countries
• Despite the remarkable progress achieved during the last decade in terms of acquisition of novel technologies, equipment and staffing, medical physics in developing countries is still well below the level required to provide adequate professional support to clinical diagnostic imaging and radiation therapy facilities available today.
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• Africa is the least developed continent with respect to medical physics resources in terms of equipment and qualified professional staff, and requires particular attention. The basic needs in the delivery of healthcare are still profound in this part of the world. An analysis of available resources for medical physics support in these countries is urgently needed to serve as a baseline to plan future development This is indeed very hard to realize in practice, given the lack of reliable information and the rather obscure channels followed to plan and build new infrastructures and to acquire costly equipment in many of these countries.
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• A common facet shared by developing countries is that radiation protection procedures are not as heavily regulated as in developed countries and radiotherapy/diagnostic imaging facilities are less computerized. The lack of standard electronic patient record handling utilities available today in modern healthcare facilities is also worth emphasizing given its negative impact on the daily management of patients and the availability of reliable statistics. Private facilities are limited and are, in general, prohibitively expensive for the average person in these economically depressed nations.
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• . The fraction of patients who receive indicated treatment is further reduced by social and economic factors and unflavored individuals are denied services. Availability of radiation therapy and diagnostic imaging facilities is usually concentrated in the capital cities; besides, the local governments recognize the need to decentralize medical care. Many barriers, both practical and organizational, stand between the patient and necessary care.
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• These problems of availability and needed implementation of strategies for cancer diagnosis and treatment are common in developing countries. From my own experience, it would appear that the optimization of current resources is more important than obtaining additional equipment and resources. Adequate education, training and application of standard diagnostic and therapeutic approaches and techniques should improve healthcare delivery.
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• The IOMP, through its statutes, encourages the worldwide establishment of professional medical physics societies and puts particular effort into stimulating their creation and growth in developing countries Among the objectives of national medical physics societies is to provide information and guidance on the training, responsibilities, organizational relationships, and roles of qualified staff in the field of medical physics.
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• The major and most serious problem facing most of these societies is the absence of a professional status for medical physicists. This remains a major hurdle even in some countries from the developed world, following the refusal of the International Labor Organization (ILO) to recognize this profession (sequent to extensive lobbying by the IOMP) and to include it in the ILO classification of professions. In order to upgrade to such a status, it is necessary to make it a legal requirement that all radiation medicine facilities should employ medical physicists.
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• In its Malaga declaration, the European Federation of Organizations of Medical Physics (EFOMP) states that medical physics should be considered a ‘regulated healthcare profession’. Again this is far from being the rule even in developed nations, where the presence of a qualified medical physicist is legally required only in radiation therapy facilities.
• One area of concern in most developing countries is that the number of qualified and experienced medical physicists per million of the population in the most important disciplines including radiotherapy, diagnostic radiology and nuclear medicine, is very low compared to levels achieved in Europe, for example.
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• It has recently been realized in developed nations that the shortage of qualified medical physicists is a serious problem that requires particular attention. The problem is catastrophic in developing countries, where some radiation therapy facilities and almost all diagnostic imaging units do not have access to expert physics support. The EFOMP survey shows that the number of trained medical physicists (per million inhabitants) in Europe nowadays
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• nowadays reaches 6 in radiation physics, 5 in nuclear medicine and 4 in diagnostic radiology. African countries present the lowest number of physicists per million of the population. This shortage requires very urgent attention by decision makers who should establish policies to limit the brain drain of qualified scientists or at least keep it to a reasonable level and to encourage the establishment of national medical physics societies to enable the growth of this specialty.
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• In a critical appraisal of the role of medical physicists in the developed world, Prof. S. Webb advocated that “medical physicists need to be actually doing medical physics, not spending too much time on administration, business, grant writing, scientific politics and unnecessary committee and professional society work” … “They should at the very least, stay active part-time research workers and/or clinical service scientists.” This also applies to medical physicists practicing in developing countries. However, the situation is always more complicated and the problems (including turf battles) faced in these regions of the world more difficult to handle.
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• . Medical physicists should be talented and have plenty of additional skills to be able to handle these issues efficiently. They should also be clever, diplomatic and excellent communicators to convince their administrators (usually inexpert in applications of physical sciences in medicine) about the importance of their work and its implications on healthcare delivery
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Summary and future prospects
• The past century was the century of "big hit science" for medical physics where major discoveries and inventions were brought to the world by brilliant scientists that revolutionised the practice of medicine. Medical physics is not an undemanding and easy profession, and should never be considered as a ‘stomach job’ used to earn its living, but instead as a passion that should be given the place it deserves in our lives
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• instead as a passion that should be given the place it deserves in our lives. We all recall the words of late Prof. Abdus Salam (1979 Nobel Laureate in Physics), who said that scientists are very happy people because their job is also their hobby. It goes without saying that this is the example that physicists from developing countries should follow. Novel technologies are driving the growth of healthcare delivery and cutting-edge biomedical research. Yet developing countries will not likely have a chance to access these technologies in the near future.
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• Contrary to the opinions claiming that it is the duty of developed governments to translate and adapt those novel techniques to the particular needs of developing countries, I strongly believe that it is the role of the countries needing these technologies to acquire the knowledge required for translation and adaptation, as this task is not the priority for developed nations, where young medical physicists practicing in these countries are focused on building their careers.
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• Government officials can play a very important role by establishing effective long-term policy goals for physics support in healthcare institutions. Issues such as providing an adequate budget for training support and proper equipment can have a profound impact on healthcare services. Staffing levels may not depend on bed size, as compared to developed nations, since the average hospital in those countries has much more equipment compared to a hospital of the same size in a developing country.
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• In many developing countries, the first need is to provide high quality physics support in clinical routine. National medical physics societies that already exist can play an important role in creating awareness and proper communications with higher authorities. Organizing lectures, support to users, establishing policies and guidelines, all while assuring good productivity and motivation through objective methods, can have a positive impact. In view of the actual situation, there are still some political lessons to be learned.
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• One important issue that needs to be stressed is the inclusion of national scientific non-governmental organisations in cooperation programs to control the efficient use of money and equipment. Education and training requirements for medical physicists should be harmonized around the world. This can be achieved only if local governments and national organisations adhere to such a project. Scientific information should not be “owned” but be freely available through the usual channels.
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• Continuing efforts are needed to bridge the gap between developing and developed countries. In this regard, establishment of guidelines for proper medical physics education and clinical support in developing countries are urgently needed.
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Thank u
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