What Goes into Planning Your Radiation Therapy
When your cancer care team plans your radiation therapy, they look at many things, including your cancer type and stage, treatment goals, and overall health. This helps them decide the best type of radiation therapy for you.
Understanding how these decisions are made can help you feel more informed and prepared.
How radiation therapy works with other treatments
Sometimes, radiation is the only treatment you need (primary treatment). More often, it’s used along with surgery, chemotherapy (chemo), or both. Sometimes it’s used with other treatments, like targeted therapy, hormone therapy, and immunotherapy.
For example, radiation may be used:
- To shrink a tumor before surgery or chemo (called neoadjuvant therapy).
- After surgery or chemo to help kill any remaining cancer cells in the body (called adjuvant therapy).
- With other treatments if cancer comes back or doesn't completely go away.
Who gives radiation therapy treatments?
During your radiation therapy, a team of highly trained medical professionals will care for you. Your team may include these people:
- Radiation oncologist: A doctor specially trained to treat cancer with radiation. They oversee your radiation treatment plan.
- Radiation oncology advanced practice providers: A nurse practitioner (NP) or physician associate/assistant (PA) who works with the radiation oncologist to care for you during radiation.
- Radiation physicist: Makes sure the radiation equipment is working as it should and that it gives you the exact dose prescribed by your radiation oncologist.
- Dosimetrist: Helps the radiation oncologist plan the treatment.
- Radiation therapist or radiation therapy technologist: Operates the radiation equipment and positions you for each treatment.
- Radiation therapy nurse: A nurse with special training in cancer treatment. They can give you information about radiation treatment and managing side effects.
You might also see a dietitian, physical therapist, speech therapist, social worker, dentist or dental oncologist, pharmacist, or other health care providers.
Planning your radiation treatment (simulation)
Radiation is planned and given by a trained cancer care team (see above).
Before starting radiation therapy, your radiation oncologist will examine you, review your medical history and test results, and pinpoint the exact area to be treated.
This planning session is called simulation. You might hear it called the sim.
What happens during the sim?
You’ll be asked to lie still on a table while the radiation therapist uses imaging scans (like a CT scan or MRI) to define your treatment field (also called the treatment port). These are the exact places on your body where the radiation beams will be aimed.
The simulation is very important and may take some time. It's used to plan the exact location of the treatment, on or in your body. The radiation can then be delivered to the tumor as directly as possible while affecting healthy tissues as little as possible.
Placing a fiducial (before the sim)
Sometimes, a marker is placed inside your body before the simulation. This marker is called a fiducial. It is small and often made of metal. It helps your care team deliver radiation as accurately as possible.
The fiducial might be placed by another doctor, during a separate procedure before the sim. It usually stays in your body after radiation treatment, but you won’t be able to feel it.
Molds, casts, masks, and markings
One or more of these things might also happen during your simulation:
- Making a mold, mask, or cast: A special mold, mask, or cast of a body part might be made. This is to help you stay still during treatment and make sure you are in the same position each time.
- Marking the treatment field: The radiation therapist might mark the treatment field with freckle-sized dots of semi-permanent ink. These usually fade away over time, but they need to stay on your skin until you finish treatment. Don’t scrub these marks or use soap on them.
- Marking with permanent dots: Sometimes, the area is marked with permanent dots like a tattoo. (These can be removed later with a laser.)
Choosing the right radiation dose
The radiation oncologist works with other members of the care team to decide how much radiation you need, how it will be given, and how many treatments you should have. They use a lot of information, including your cancer type, your simulation, and other tests.
They also base this on research that shows the minimum and maximum dose of radiation for the type of cancer and the area of the body being treated.
Deciding to give more radiation (re-irradiation)
If the cancer doesn’t completely go away after radiation treatment, or if it comes back, you might need more treatment. The radiation team will decide whether more radiation therapy is the best option.
Getting radiation again to the same area is called re-irradiation.
This decision depends on the type of cancer, where the tumor is, and how much radiation has already been given to the area. If the maximum dose has already been reached, radiation might not be the best option. You may be offered other treatment instead.
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- References
Developed by the American Cancer Society medical and editorial content team with medical review and contribution by the American Society of Clinical Oncology (ASCO).
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Last Revised: June 9, 2025
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