Alopecia (al-oh-PEE-she-ah): Hair loss.

Anesthesia: Loss of feeling or sensation resulting from the use of certain drugs or gases.

Antiemetic (an-tee-eh-MET-ik): A medicine to prevent or relieve nausea or vomiting.

Benign tumor: A growth that is not a cancer and does not spread to other parts of the body.

Biological therapy: Treatment by stimulation of the body's immune defense system.

Biopsy: The removal of a sample of tissue to see whether cancer cells are present.

Brachytherapy (BRAK-ee-THER-ah-pee): Internal radiation treatment achieved by implanting radioactive material directly into the tumor or very close to it. Sometimes called "internal radiation therapy".

Cancer: A general term for more than 100 diseases that have uncontrolled, abnormal growth of cells that can invade and destroy healthy tissues.

Catheter: A thin, flexible tube through which fluids enter or leave the body.

Chemotherapy: Treatment with anticancer drugs.

Cobalt 60: A radioactive substance used as a radiation source to treat cancer.

Dietician (also registered dietician): A professional who plans diet programs for proper nutrition.

Dosimetrist (do-SIM-uh-trist): A person who plans and calculates the proper radiation dose for treatment using a treatment planning computer system.

Electron beam: A stream of particles that produces high-energy radiation to treat cancer.

External radiation: Radiation therapy that uses a machine located outside of the body to aim high-energy rays at cancer cells.

Fluoride: A chemical applied to the teeth to prevent tooth decay.

Fractionation: Dividing the total dose of radiation into smaller doses in order to give healthy tissue time to repair itself.

Gamma rays: High-energy rays that come from a radioactive source such as a cobalt-60.

Gray: A measurement of absorbed radiation dose; 1 Gray = 100 rads.

High-dose-rate remote brachytherapy: A type of internal radiation in which each treatment is given in a few minutes while the radioactive source is in place. The source of radioactivity is removed between treatments. Also known as high-dose-rate remote radiation therapy.

Hyperfractionated radiation: Division of the total dose of radiation into smaller doses that are given more than once a day.

Implant: A small container of radioactive material placed in or near a cancer.

Internal radiation: A type of therapy in which a radioactive substance is implanted into or close to the area needing treatment.

Interstitial radiation: A radioactive source (implant) placed directly into the tissue (not in a body cavity).

Intracavitary radiation: A radioactive source (implant) placed in a body cavity such as the chest cavity or the vagina.

Intraoperative radiation: A type of external radiation used to deliver a large dose of radiation therapy to the tumor bed and surrounding tissue at the time of surgery.

Linear accelerator: A machine that creates high-energy radiation to treat cancers, using electricity to form a stream of fast-moving subatomic particles. Also called megavoltage (MeV) linear accelerator or a linac.

Malignant: Cancerous (see cancer).

Medical oncologist: A doctor who specializes in using chemotherapy to treat cancer.

Metastasis: The spread of a cancer from one part of the body to another. Cells in the second tumor are like those in the original tumor.

Oncologist: A doctor who specializes in treating cancer.

Oncology: The branch of medicine devoted to the diagnosis and treatment of cancer.

Palliative Care: Treatment to relieve, rather than cure, symptoms caused by cancer. Palliative care can help people live more comfortably.

Physical therapist: A health professional trained in the use of treatments such as exercise and massage.

Platelets: Special blood cells that help stop bleeding.

Port (also treatment field): The area of the body through which external beam radiation is directed in order to reach a tumor.

Prosthesis: An artificial replacement of a part of the body.

Protraction: The period of time during which a course of radiation is given.

Rad: Short form for "radiation absorbed dose"; a measurement of the amount of radiation absorbed by tissues (100 rad = 1 Gray).

Radiation: Energy carried by waves or a stream of particles.

Radiation oncologist: A doctor who specializes in using radiation to treat cancer.

Radiation oncology nurse: A registered nurse or licensed practical nurse who has extensive training in oncology and radiation therapy.

Radiation physicist: A person trained to ensure that the radiation machine delivers the right amount of radiation to the treatment site.

Radiation therapist: A person with special training who runs the equipment that delivers the radiation.

Radiation therapy: The use of high-energy penetrating rays or subatomic particles to treat disease. Types of radiation include x-ray, electron beam, alpha and beta particles, and gamma rays. Radioactive substances include cobalt, radium, iridium, and cesium. (See also gamma rays, brachytherapy, teletherapy, and x-ray.)

Radioisotope: A radioactive form of an element.

Radiologist: A physician with special training in reading diagnostic x-rays and performing specialized x-ray procedures.

Radioresistance: When cells do not respond easily to radiation.

Radiosensitivity: How susceptible a cell, cancerous or healthy, is to radiation. Cells that divide frequently are especially radiosensitive and are more affected by radiation.

Radiotherapy: See radiation therapy.

Remote brachytherapy: See high-dose-rate remote brachytherapy. Sealed radiation source: A metal seed or capsule containing a radioisotope, used for brachytherapy procedures.

Simulation: A process involving special x-ray pictures that are used to plan radiation treatment so that the area to be treated is precisely located and marked for treatment.

Social worker: A mental health professional with a master's degree in social work (MSW). A social worker can provide assistance in dealing with medical, psychological, social, and educational needs.

Teletherapy: Treatment in which the radiation source is at a distance from the body. Linear accelerators and cobalt machines are used in teletherapy.

Treatment port or field: The place on the body at which the radiation beam is aimed.

Tumor: An abnormal mass of tissue. Tumors are either benign or malignant.

Unsealed internal radiation therapy: Internal radiation therapy given by injecting a radioactive substance into the bloodstream or a body cavity. This substance is not sealed in a container.

White blood cells: The blood cells that fight infection.

X-ray: High-energy radiation that can be used at low levels to diagnose disease or at high levels to treat cancer.