Glossary of radiation therapy terms


At the beginning of any cancer journey, you’ll hear doctors, nurses and even your peers using terms you may have never heard of before and it’s overwhelming. It’s always good to ask your oncology team to explain if they are using terms that you do not understand. We’ve put together this list of common radiation oncology terms as a resource to help you understand the language of radiation therapy.

The list of treatment-related words is long. If you’re looking for something that isn’t on our list, we recommend checking with the American Cancer Society or writing them down to ask your radiation team during your next visit.

Accelerated radiation: A radiation therapy schedule in which the total dose of radiation is administered over a shorter period of time. It is becoming more common as a treatment plan for breast cancers.

Adjuvant therapy: A treatment that is given after the primary treatment is completed to reduce the risk of cancer coming back.

Applicator: A device used to administer internal radiation therapy or brachytherapy. The applicator holds a radioactive source in place for the duration of the treatment.

Beam films: Pictures that are taken before and throughout treatment to check the position of the radiation beams and confirm that treatment is being administered to the correct place. Beam films may also be called port films.

Boost: After an initial course of radiation, a boost may be given in to increase control and reduce the risk or recurrence.

Brachytherapy or implant: A type of internal radiation therapy in which radioactive sources, sometimes called seeds, are placed inside or next to a tumor for a predetermined amount of time.

Centigray: A metric used to measure the amount of radiation dose absorbed by the body.

Conformal radiation therapy: A type of treatment that uses computers to create a 3-D picture of the tumor to accurately deliver the highest dose of radiation while sparing healthy tissue as much as possible.

Dosimetrist: A person who has knowledge of radiation treatment machines and equipment, understands treatment procedures and has the education and expertise to plan and calculate the proper radiation doses for treatment. Dosimetrists are the behind-the-scenes radiation oncology team members working closely with doctors and physicists to care for patients.

Electron beam: A stream of high-energy particles called electrons used to treat cancer.

External radiation: A radiation therapy where high-energy rays are administered with a machine located outside the body most commonly using a linear accelerator. External radiation is the most common form of radiation treatment.

Fractionation: Refers to a division of the total radiation dose into smaller doses that will reduce the potential for radiation exposure to healthy tissue. 

Fractions: The dose of radiation that is divided from the total radiation to be given each day.

Gamma rays: A very penetration form or electromagnetic radiation.

High-dose-rate (HDR) brachytherapy: A type of internal radiation therapy that delivers radiation close to, or inside, the tumor(s) in the body. HDR Brachytherapy can be used as a standalone treatment or after a tumor has been surgically removed to eliminate any remaining cancerous cells.

Hyperfractionated radiation: A radiation schedule in which the total dose of radiation is fractionated into even smaller doses to be administered multiple times a day over the standard period of time.

Image-guided radiation therapy or IGRT: A more-accurate radiation therapy that uses a computer to create an image of a tumor to guide the radiation beam during treatment. IGRT uses CT, ultrasound, X-ray and other imaging techniques.

Intensity-modulated radiation therapy or IMRT: 3-dimensional radiation therapy that reduces healthy tissue’s exposure to radiation by using computer-generated images to show a tumor’s size and shape. Radiation is administered at different intensities and aimed at the tumor from multiple angles.

Internal radiation: A type of internal radiation therapy in which radioactive sources, sometimes called seeds, are placed inside or next to a tumor for a predetermined amount of time. Also called brachytherapy.

Linear accelerator or linac: A machine that is used to deliver radiation during treatment.

Palliative care or palliation: Care given to patients who have a serious or life-threatening disease to improve their quality of life. Palliative care can include treating side effects caused by disease treatment and caring for psychological, social and spiritual needs.

Port: The part of the body that external beam radiation is directed through to reach cancer cells or a tumor. Only a specific amount of radiation is beamed at the target area. It is important that the radiation port is aligned with the radiation machine for each treatment. The port may also be called the treatment field.

Port films: Pictures that are taken before and throughout treatment to check the position of the radiation beams and confirm that treatment is being administered to the correct place. Port films may also be called beam films.

Radiation oncologist: A medical specialist doctor who is trained in the use of radiation therapy for the treatment of cancer.  A Radiation oncologist assesses each patient and determines the best management plan. They oversee treatment and monitor progress. They work closely with the radiation therapist and physicist to ensure safe and accurate treatment.

Radiation physicist: A person who oversees radiation treatments and X-ray machines to ensure that the machines deliver the correct amount of radiation to the right location. Physicists work with radiation oncologists to form the treatment plan ensuring that the schedule and dose will have the best chance of killing cancer cells.

Radiation therapist: A person who is trained to administer a prescribed dose of radiation to patients and record the patient’s medical information. Radiation therapists document reactions to treatment if there are any, answer questions from the patient and work closely with the oncology team throughout treatment.

Radiation therapy nurse: A nurse who supports a patient and the radiation oncology team during treatment. A radiation nurse might assess a person’s overall health, help navigate complex medical systems and educate patients. They have a good understanding of general medicine and radiation therapy.

Radiation therapy or radiotherapy: The use of radiation to treat cancer and other diseases. Radiation may be administered externally from a machine outside the body, or internally with radioactive material placed in the body near cancer cells.

Simulation: A process used to plan radiation therapy to determine and mark the precise target area to allow the radiation to be delivered to the intended location.

Treatment plan: A schedule and prescription describing how a person should be treated with radiation. The entire radiation oncology team works together using special software to maximize radiation to cancer cells and tumors while sparing healthy tissue.