R115777: An anticancer drug that inhibits the transformation of normal cells to cancer cells. It belongs to the family of drugs called enzyme inhibitors.

Radiation fibrosis (ray-dee-AY-shun fye-BRO-sis): The formation of scar tissue as a result of radiation therapy.

Radiation oncologist (ray-dee-AY-shun on-KOL-o-jist): A doctor who specializes in using radiation to treat cancer.

Radiation surgery: A radiation therapy technique that delivers radiation directly to the tumor while sparing the healthy tissue. Also called radiosurgery and stereotactic external beam irradiation.

Radiation therapy (ray-dee-AY-s (ray-dee-AY-shun): The use of high-energy radiation from x-rays, gamma rays, neutrons, and other sources to kill cancer cells and shrink tumors. Radiation may come from a machine outside the body (external-beam radiation therapy), or it may come from radioactive material placed in the body in the area near cancer cells (internal radiation therapy, implant radiation, or brachytherapy). Systemic radiation therapy uses a radioactive substance, such as a radio-labeled monoclonal antibody, that circulates throughout the body. Also called radiotherapy.

Radical cystectomy (RAD-ih-kal sis-TEK-toe-mee): Surgery to remove the bladder as the bladder as well as nearby tissues and organs.

Radical mastectomy (RAD-ih-kal mas-TEK-toe-mee): Surgery for breast cancer in which the breast, chest muscles, and all of the lymph nodes under the arm are removed. For many years, this was the operation most used, but it is used now only when the tumor has spread to the chest muscles. Also called the Halsted radical mastectomy.

Radical prostatectomy (RAD-ih-kalpros-ta-TEK-toe-mee): Surgery to remove the entire prostate. The two types of radical prostatectomy are prostatectomy and perineal prostatectomy.

Radioactive (RAY-dee-o-AK (RAY-dee-o-AK-tiv): Giving off radiation.

Radioactive iodine: A radioactive form of the chemical element iodine, often used for imaging tests or as a treatment for cancer.

Radiofrequency ablation: The use of electrical current to destroy tissue.

Radio immunoguided surgery: A procedure that uses radio-labeled substances to detect tumors for surgical for surgical removal.

Radioimmunotherapy: Treatment with a radioactive substance that is linked to an antibody that will attach to the tumor when injected into the body.

Radioisotope: An unstable element that releases radiation as it breaks down. Radioisotopes can be used in imaging tests or as a treatment for cancer.

Radiolabeled: Any compound that has been joined with a radioactive substance.

Radiologist (RAY-dee-ol-o-jist): A doctor who specializes in creating and interpreting pictures of areas inside the body. The pictures are produced with x-rays, sound waves, or other types of energy.

Radiology: The use of radiation (such as x-rays) or other imaging technologies (such as ultrasound and magnetic resonance imaging) to diagnose or treat disease.

Radionuclide scanning: A test that produces pictures (scans) of internal parts of the body. The person is given an injection or swallows a small amount of radioactive material; a machine called a scanner then measures the radioactivity in certain organs.

Radiopharmaceuticals: Drugs containing a radioactive substance that are used in the diagnosis and treatment of cancer and in pain management of bone metastases. Also called radioactive drugs.

Radiosensitization: The use of a drug that makes tumor cells more sensitive to radiation therapy.

Radiosensitizers: Drugs that make tumor cells more sensitive to radiation.

Radiotherapy (RAY-dee-o-THER-a-pee): The use of high-energy radiation from x-rays, neutrons, and other sources to kill cancer cells and shrink tumors. Radiation may come from a machine outside the body (external-beam radiation therapy) or from materials called radioisotopes. Radioisotopes produce radiation and can be placed in or near the tumor or in the area near cancer cells. This type of radiation treatment is called internal radiation therapy, implant radiation, interstitial radiation, or brachytherapy. Systemic radiation therapy uses a radioactive substance, such as a radio-labeled monoclonal antibody, that circulates throughout the body. Radiotherapy is also called radiation therapy, irradiation, and x-ray therapy.

Radon (RAY-don): A radioactive gas that is released by uranium, a substance found in soil and rock. When too much radon is breathed in, it can damage lung cells and lead to lung cancer.

Raloxifene: A drug that belongs to the family of drugs called selective estrogen receptor modulators (SERMs) and is used in the prevention of osteoporosis in postmenopausal women. Raloxifene is also being studied as a cancer prevention drug.

Raltitrexed: An anticancer drug that inhibits tumor cells from multiplying by interfering with cell interfering with cells' ability to make DNA. Also called ICI D1694.

Randomized: Describes an experiment or clinical trial in which animal or human subjects are assigned by chance to separate groups that compare different treatments.

Randomized clinical trial: A study in which the participants are assigned by chance to separate groups that compare different treatments; neither the researchers nor the participants can choose which group. Using chance to assign people to groups means that the groups will be similar and that the treatments they receive can be compared objectively. At the time of the trial, it is not known which treatment is best. It is the patient's choice to be in a randomized trial.