The only person who can legally give medical treatment is a licensed physician. But there are many professionals who assist the physician to carry out a medical treatment. Nurses, technologists, physician assistants and aids all play a vital role in helping the physician carry out a medical treatment. Some of these professionals are never seen by the patient.

In radiation oncology – a specialty that uses precisely defined radiation beams to treat cancers – many of the same people are there to help the patient. However, because of the complex equipment used to generate the radiation beams and apply them most effectively, physicists are also part of the team.

Since shortly after a physicist named Roentgen discovered X-rays in 1895, physicists have worked alongside physicians in planning and implementing radiation therapy. Complex machines, like the one in Figure 1, can produce many different radiation beams in many different shapes. The physicist, in this case a medical physicist, is expected to precisely define these beams through sophisticated measurements, and must accurately model them in special planning computers that allow choosing beam arrangements specifically for each patient.

Figure 2 is a photograph of such a plan. It uses CT scans of the patient that are corrected for tissue density to allow computer modeled beams to be placed and manipulated until the distribution of radiation dose is deemed acceptable by the physician.

When approved, this plan is sent to the treatment machine where technologists, called therapists, set up the patient according to the plan. The settings on the machine must be determined and approved by the medical physicist who also maintains the beams calibration and checks each patient’s chart weekly to verify that the treatment is properly implemented.

Medical physicists require a post-graduate education to at least the master’s degree and more preferably to the Ph.D. level, followed by mentored training in the clinic for at least two years. Medical physicists are the only non-physicians who are certified to practice by a medical board. Certification, after deemed eligible, requires examinations over a two-year period by the American Board of Radiology, the same medical board that certifies the physician in radiation oncology. Also, as with most medical specialists, the state requires that they are licensed.

In effect, the physician determines which part of a patient is to be treated and to what dose, while the medical physicist is responsible for seeing that this prescription is implemented as designed. Each of the support staff plays a part in this process.

More than half of all cancer patients receive radiation therapy sometime during their treatment. Medical physicists play an important role in accurately delivering those treatments even though the patient may never see them.