Radiation Therapy
Radiation therapy uses high-energy x-rays to treat diseases such as cancer. When living cells are exposed to radiation they become less able to multiply and reproduce. Malignant cells are more susceptible to radiation than normal cells, thus as tumor cells gradually dwindle, normal cells recover and rebuild. This unequal effect of radiation on malignant cells and healthy cells forms the basis of therapeutic radiation.
Ever since Marie Curie discovered radium in the 19th century, radiation has been shown to cause cancers to regress or shrink. Initially used in large cancers that could not be surgically removed, radiation therapy has been refined over the last several decades to become a sophisticated form of treatment effective on several types of cancer.
How Radiation Treats Cancer
Radiation is a local or regional form of cancer therapy. It is applied to the specific area of the body that contains the tumor, unlike chemotherapy which is given by injection or by mouth and travels throughout the entire body. Both radiation and chemotherapy inhibit cell growth and reproduction but usually do so at slightly different points within the cell reproductive cycles, thus both therapies can be combined for a greater effect.
As it is a local treatment, radiation has advantages over chemotherapy. It is less likely to cause general side-effects (such as nausea, extreme fatigue, or decrease of blood cell counts) but it cannot treat disease that has spread beyond the local area.
Note that radiation and chemotherapy do not compete against each other. Some diseases lend themselves well to radiation therapy, others to chemotherapy, while others require a combination of radiation and chemotherapy. Surgery also is an important method of treatment and can be used before or after radiation or chemotherapy.
When used properly, radiation is a very potent tool in the oncologist's arsenal for arresting cancer growth. It is estimated that at least 50% of all cancer patients need radiation some time in the course of their illness.
Safety
According to the experience medicine has gained over the last three decades, radiation is safe when used correctly. Doctors have learned to strike a reasonable balance between tumor control and side-effects. Doses are very strictly controlled. Safety interlocks and monitoring devices are extensively built into all therapy machines. Radiation equipment is calibrated on a regular basis as dictated by government regulations. Radiation oncologists are required to have completed a fully-accredited post-M.D. residency in the field of radiation therapy. Technologists who operate the equipment under the doctors' orders are certified and licensed by the State.
If the patient has also had surgery and/or chemotherapy, side-effects from radiation can be more pronounced. This is where the training and experience of the radiation oncologist are critical, as the dose and scheduling of radiation may have to be adjusted.
Treating Tumors
Most types of cancer respond to radiation. Those that "shrink" rapidly are termed radiosensitive, others that don't are called radioresistant. However, even radioresistant tumors can respond if additional therapy is given to a higher dose.
Not surprisingly, radiosensitive tumors can be cured with radiation. These include cancers of the prostate, breast, cervix, vocal cords, tonsil, mouth, thyroid, rectum / anus, and skin (except malignant melanoma).
Other, less sensitive, tumors can be treated with radiation for palliation, which means to decrease the size of the tumor, reduce pain, control bleeding, and thus to prolong lives or improve quality of life for patients with tumors considered incurable.
Note that some cancers which were considered incurable only a few years ago, now can be effectively controlled with newer treatment programs using a combination of surgery, newer chemotherapy drugs, and radiation - each exploiting its own specific advantages.