Besides the adequacy of physics staffing in terms of number of personnel in relation to the patient load or equipment, education and training of these personnel are of critical importance. The greatest weakness in this regard has been the physicist’s training. Most physicists are hired with less than adequate clinical training. Structured clinical training programs have been traditionally nonexistent. Certification boards for physicists exist, but the entry requirements for the examination still do not mandate residency-type clinical training as is required of the physicians. As a result, there is an unchecked influx of inadequately trained physicists into the field.

The physicist’s training problems are being addressed at the national level (9,10,11). Physics residency programs are being instituted, although at a much slower pace than needed. It is hoped that eventually all clinical medical physicists will be required to go through nationally accredited residency programs before taking the board examinations or assuming independent clinical responsibilities. Recently, the American Board of Radiology (http://www.theabr.org)—the certifying board for radiological physicists—has decided that “Beginning in 2014… candidates must be enrolled in or have completed a CAMPEP [Commission on Accreditation of Medical Physics Educational Programs] accredited residency program.”

Just as formalized clinical training is important for physicians and physicists, it is also important for dosimetrists. The American Association of Medical Dosimetrists has formalized the training of dosimetrists by establishing training curricula, accreditation, and professional certification.

Qualifications of a clinical medical physicist have been debated in the past, but recently a consensus has developed among the various national organizations. A radiation oncology physicist is considered qualified if he or she has an M.S. or Ph.D. degree in physics, medical physics, or a closely related field and a certification in radiation oncology physics by the American Board of Radiology, the American Board of Medical Physics, or another appropriate certifying body.

A qualified medical dosimetrist has a minimum of a high school diploma and a certification by the American Association of Medical Dosimetrists. Most certified dosimetrists also are certified radiation therapy technologists.

The roles and responsibilities of the physics team have been discussed in the literature (11,12,13) and are summarized in Table 17.2. As emphasized previously, the physicist must direct the physics team and assume full responsibility of the physics data and procedures applied to the patients, irrespective of whether these activities are carried out by the physicist, dosimetrist, or other personnel. This unambiguous responsibility of physics procedures by the physicist is based on the same rationale as the physician’s control of medical prescription. Nonconformity to this principle can pose a serious risk to the patient.

The radiation oncologist undoubtedly has the overall responsibility for the conduct of the entire treatment process. Because of that role, it is his or her responsibility to ensure that an adequate and competent physics team is in place and that the roles of different personnel on the team are appropriately defined. It has been recognized that inadequacy of physics support translates into substandard or less than optimal patient care (4,6).

Calibration of radiation generators or sources is the exclusive responsibility of the medical physicist. No other personnel has the expertise to perform this most critical function. Because of the absolute necessity of the calibration procedure before the machine can be released for patient treatment, all institutions manage to acquire physics support at least sufficient to provide periodic calibration of the radiation equipment. However, these periodic calibrations, outside of a well-structured quality assurance program, are inadequate and cannot ensure continued safety of machine operation on a daily basis (14).

Next to calibration and quality assurance of radiation equipment is the physicist’s role in treatment planning. Although the treatment-planning process involves sophisticated physics concepts in designing and optimizing patient treatments, most institutions do not involve physicists sufficiently in this process. As discussed previously (Fig. 17.1), some physicians tend to work alone or with dosimetrists to design treatment plans. It should be realized that the absence of a physicist from the treatment-planning scene takes away an important element of quality control, namely the optimization and scientific authentication of the treatment plan. The physicist’s direct involvement in the treatment-planning process is possible only if the consultation is sought by the radiation oncologist. If the latter is not accustomed, by training or experience, to such interactions, the physicist is not brought into the treatment-planning loop. Consequently, an important member of the treatment-planning team is bypassed.

At some institutions, the physicist’s role in treatment planning has been made indispensable. For example, at the University of Minnesota the physicist’s consultation is made as important as other consultations, such as those sought from the medical oncologist, the surgeon, or the radiologist. To prevent bypassing the physics consultation, each patient is assigned a physicist who is available at the time of simulation to assist the radiation oncologist in formulating the best possible treatment plan. Subsequent physics work is the designated physicist’s responsibility, although he or she may be assisted by the dosimetrist or other technical personnel. The final treatment plan is approved by the radiation oncologist after discussing the plan with the physicist. Also, the physicist is present at the time of first treatment and subsequent treatments, if needed, to ensure proper implementation of the plan.

Not all the clinical physics procedures need to be performed by physicists. Many of the technical tasks can be delegated to dosimetrists so that physicists can devote time to essential developmental activities. Every radiation oncology department needs to develop new programs as well as revise the old ones to keep current with advancements in the field. Responsibility often rests with the physicist to implement these advances while maintaining the quality of care. Examples from the past three decades include development of linear accelerator technology, computer imaging, 3-D treatment planning, conformal and dynamic therapy, and remote afterloading brachytherapy. Whereas these technologies were not developed exclusively by physicists, they had an important role in their design and clinical application. Along with these major advancements came the innovations in treatment techniques, for example, mantle fields, total body irradiation, electron beam therapy, intensity-modulated radiation therapy, stereotactic radiosurgery, low-energy source brachytherapy, and high dose rate brachytherapy. These refinements form an integral part of the physicist’s responsibilities and are often not separated from his or her routine clinical duties. It is, therefore, important to recognize the need for providing sufficient technical support to the physicist for a proper fulfillment of his or her role.

The type or quality of radiation beam is dictated by the type and location of cancer to be treated. Most head and neck cancers can be treated with low-energy megavoltage units: cobalt-60 or linear accelerators in the energy range of 4 to 6 MV. That does not mean that a facility equipped with only one of these units is capable of providing quality care to all patients with head and neck cancers. On the contrary, institutions whose sole treatment equipment is one of these units are not in a position to undertake complex and sophisticated treatment techniques required for most head and neck cancers. Depending on the kind and stage of the disease, an optimal treatment plan may call for other types of beams such as a combination of low- and high-energy photon beams or an electron beam. A facility equipped with a single-energy beam tends to follow suboptimal treatment plans or obsolete treatment techniques when the best available radiation therapy equipment is a cobalt unit.

Because of the wide variety of cancers normally seen in a radiation therapy clinic, it is necessary to have at least two qualities of photon beams: a low-energy (cobalt-60 or 4- to 6-MV x-rays) and a high-energy (10 MV or higher) beam. In addition, electron beams of several different energies between 6 and 20 MeV must be available because approximately 30% of patients require an electron beam for boost or an entire course of treatment.

A dual-energy linear accelerator can provide all the beams necessary for modern radiation therapy. These machines are usually equipped with one low- and one high-energy photon beam and a number of electron energies up to 18 or 20 MeV. That provides sufficient capability to treat any cancer that needs external beam. In addition, accelerators must be equipped with on-board imaging equipment to ensure accurate delivery of treatments, especially when using highly conformal techniques such as IMRT and IGRT.

Additional machines are required if the patient load exceeds about 30 patients per day. Although it is possible to treat more than 30 patients per machine per day, higher patient loads necessitate
hurried treatments and consequently allow less attention to detail. It is important for a radiotherapy facility to be equipped not only with appropriate type and quality of beams, but also with a sufficient number of machines to handle the patient load.

Certain cancers need brachytherapy, usually in combination with external beam. Cancer of the uterine cervix and some other gynecologic malignancies are best treated with these techniques. Unless the center has the policy not to treat patients for whom the brachytherapy is the treatment of choice, brachytherapy equipment must be available to provide quality care to patients who need this form of therapy.

For intracavitary application, radium and cesium are equally effective as far as the therapeutic effects are concerned. Cesium has replaced radium mainly on the basis of radiation protection considerations pertaining to storing and handling of these sources. For temporary interstitial implants, iridium-192 is the best available source. Iodine-125 and palladium-103 are used primarily for permanent implants such as in the prostate.

Availability of brachytherapy sources and equipment adds to the comprehensiveness of a center to provide radiation therapy. Again, if this capability is not available, a patient’s treatment may be compromised if the institution does not have a suitable alternative or rationalizes the use of external beam alone not on the basis of merit, but on the nonavailability of brachytherapy service.

Afterloading procedures are the standard of practice in brachytherapy. The therapeutic quality of the procedure is little affected by whether the afterloading is done by the bedside or remotely. An institution can provide quality brachytherapy by using conventional afterloading applicators. The need for the remote afterloaders (the low dose rate [LDR] or the HDR) is based primarily on considerations such as minimizing radiation exposure to personnel or handling large patient loads. Again, if it can be established that the remote afterloading will improve patient care (e.g., by allowing better nursing care or optimizing source placement), a case can be made to acquire such equipment. High-tech equipment such as the remote afterloaders can be very expensive and can drive up the cost of patient care. Therefore, the additional cost must be justified on the basis of cost versus patient benefit analysis.

The simulator is an essential tool for planning and designing radiation therapy treatments. Because of the poor imaging quality of the treatment beam and the logistic difficulty of obtaining time on the treatment machine, a simulator is the appropriate equipment to image the treatment fields and optimize their placement before actual treatment. Because the simulator offers the same beam geometry as the treatment machine, simulator films are used to outline the field shape and dimensions for custom-designing field blocks. The simulator room is the place where different techniques can be modeled and solutions to technical problems devised.

An essential requirement for simulation is the geometric accuracy that must be maintained at the same level as that of the treatment machine. If the simulated field cannot be accurately reproduced under the treatment machine, the whole simulation process becomes a useless exercise. Inaccurate simulation can result in erroneous treatment.

Besides the mechanical and radiation field accuracy of a simulator, its imaging quality cannot be overemphasized. Unless anatomic structures can be made visible with reasonable clarity, fields cannot be accurately outlined, negating the very purpose of simulation.

Fluoroscopic capability of a simulator is a desirable option because it allows iterative field adjustments and viewing before a final radiograph is obtained. Nonavailability of fluoroscopic option results in an increased number of film retakes and, in the long run, is not cost effective. Moreover, too many repeats could deter from optimization of the simulation process.

In addition to a radiographic simulator, a CT simulator is needed for 3-D treatment planning. A large number of CT scans taken through the region of the body to be simulated can be processed to produce a digital reconstructed radiography (DRR) in any plane. The DRR corrected for beam divergence is like the simulator radiograph, except that it is created from individual CT slices. If targets and critical structures are outlined on each CT slice, a DRR can be created to provide any simulator view with the target and the critical structures highlighted in different shades of color. The DRR view is used to optimize the design and placement of treatment fields before a simulation film is taken for verification.

With the development of treatment procedures such as IMRT, IGRT, and stereotactic radiation therapy, more and more institutions are investing in PET/CT instead of standalone CT simulators. For some cancers, fusion of PET and CT images allows greater precision in outlining planning target volume (PTV) than possible with CT alone.

A linear accelerator is a sophisticated piece of equipment that requires several months for installation, acceptance testing, and commissioning. Whereas installation is carried out by the vendor personnel, the acceptance testing and commissioning are the responsibility of the institution’s physicist. Patient treatments do not begin until the unit has been commissioned; that is, the machine tested to be acceptable and sufficient data have been acquired to permit treatment planning and dose calculations for patient treatments.