Radiation

In 1896 a German physics professor, Wilhelm Conrad Roentgen, presented a remarkable lecture entitled “Concerning a New Kind of Ray.” Roentgen called it the “X-ray”, with “x” being the algebraic symbol for an unknown quantity. There was immediate worldwide excitement. Within months, systems were being devised to use x-rays for diagnosis, and within 3 years radiation was used in to treat cancer.

In 1901 Roentgen received the first Nobel Prize awarded in physics. Radiation therapy began with radium and with relatively low-voltage diagnostic machines. In France, a major breakthrough took place when it was discovered that daily doses of radiation over several weeks greatly improved the patient’s chance for a cure. The methods and the machines that deliver radiation therapy have steadily improved since then. Today, radiation is delivered with great precision to destroy cancer tumors while limiting damage to nearby normal tissues.

At the beginning of the 20th century, shortly after radiation began to be used for diagnosis and therapy, it was discovered that radiation could cause cancer as well as cure it. Many early radiologists used the skin of their arms to test the strength of radiation from their radiotherapy machines, looking for a dose that would produce a pink reaction (erythema) which looked like sunburn. They called this the “erythema dose,” and this was considered an estimate of the proper daily fraction of radiation. It is no surprise that many of them developed leukemia from regularly exposing themselves to radiation.

Advances in radiation physics and computer technology during the last quarter of the 20th century made it possible to aim radiation more precisely. Conformal radiation therapy (CRT) uses CT images and special computers to very precisely map the location of a cancer in 3 dimensions. The patient is fitted with a plastic mold or cast to keep the body part still. The radiation beams are matched to the shape of the tumor and delivered to the tumor from several directions. Intensity-modulated radiation therapy (IMRT) is like CRT, but along with aiming photon beams from several directions, the intensity (strength) of the beams can be adjusted. This gives even more control over decreasing the radiation reaching normal tissue while delivering a high dose to the cancer.

A related technique, conformal proton beam radiation therapy, uses a similar approach to focusing radiation on the cancer. But instead of using x-rays, this technique uses proton beams. Protons are parts of atoms that cause little damage to tissues they pass through but are very effective in killing cells at the end of their path. This means that proton beam radiation can deliver more radiation to the cancer while reducing damage to nearby normal tissues.

Stereotactic radiosurgery and stereotactic radiation therapy are terms that describe several techniques used to deliver a large, precise radiation dose to a small tumor. The term surgery may be confusing because no cut (incision) is actually made. The most common site treated with this radiation technique is the brain. The linear accelerator, or a special machine known as a Gamma Knife, can be used to deliver this treatment. Research is being done to develop delivery systems to treat sites other than the brain.

Intraoperative radiation therapy (IORT) is a form of treatment that delivers radiation at the time of surgery. The radiation can be given directly to the cancer or to the adjacent tissues after the cancer has been removed. It is more commonly used in abdominal or pelvic cancers and in cancers that tend to recur (come back after treatment). IORT minimizes the amount of tissue that is exposed to radiation because normal tissues can be moved out of the way during surgery and shielded, allowing a higher dose of radiation to the cancer.

Chemical modifiers or radiosensitizers are substances that make cancer more sensitive to radiation. The goal of research into these types of substances is to develop agents that will make the tumor more sensitive without affecting normal tissues. Researchers are also looking for substances that may help protect normal cells from radiation.