Proton Radiation Therapy Treatment Process

Author: Courtney Misher, MPH, BS R.T.(T)
Last Reviewed: March 15, 2022

If proton radiation therapy might be part of your treatment plan, you will have an initial consultation where you talk to a radiation oncologist about your treatment. If you plan to have proton therapy, you will sign a consent. After this first visit, you will need to be set up for treatment. Setting you up for radiation takes many steps, many providers, and can take a few days or weeks. The following are the steps often used. These may change a little bit depending on your treatment facility.

CT Simulation

Before radiation treatments begin, you will go through a treatment planning process called "simulation." During this process, your radiation treatment team will measure your body and mark on your skin where you will receive radiation. The marks will be given with a temporary paint marker and/or a small set of permanent tattoos. The position you are in for your simulation will be the same position you will be in every day for treatment. Immobilization devices such as molds, casts, headrests, knee supports, or other devices may be used to help keep you in a comfortable position and make sure you don’t move during treatment.

A CT scan of the area being treated is done. The images from the CT scan are used to design your treatment plan and create a "map" for the treatment team. This CT scan is used only for the planning process. It is designed to work with the other equipment in the clinic. It is not a replacement for other imaging scans you have had. During your simulation, you may need contrast which is a dye that will make certain parts of your body more visible in the CT images. This can be given by drinking it (orally) or injecting it directly into your vein (intravenously).

You may be given directions if any preparation (prep) is needed before your simulation. For example, you may need your bowels to be empty so you may need to take certain medications, do an enema, or eat a certain diet. You need to follow the directions closely. If you have any questions or are having trouble doing the prep, you should call your provider.

The simulation takes about an hour. You will be lying on a hard table for the simulation and you may have some pain or discomfort. Tell the radiation therapists if you are uncomfortable right away so they can change your position. Keep in mind that the time needed to deliver the radiation therapy treatments is often much less than the time needed for the simulation.

In certain cases, an MRI or a PET scan will also be done the same day as the CT simulation. The images from these scans are also used to plan your treatment.

CT Simulator

MRI used for simulation

Technical Planning Process

After simulation, details are reviewed by the medical dosimetrists and physicists. They calculate the exact dose and course of treatment with the goal of killing the cancer while limiting dose to healthy tissue. They use proton treatment planning software to help them design the best possible treatment plan. The dosimetrist and physicist work closely with your radiation oncologist to create your treatment plan. This can take up to a week or more.

Radiation Oncologist planning a treatment.

Quality Assurance

After the radiation oncologist approves your treatment plan the physicists will check that your specific plan works on the proton machine it was created for. Once this is done you can start your radiation treatments.


You will be placed on the treatment table in the same position you were in for your simulation. The therapists will align your tattoos to the lasers in the treatment room and take a set of X-ray films or do a cone-beam computed tomography (CBCT). CBCT is an imaging technique that provides an accurate 3D representation of the body and tumor from a rotating scan. These films will be matched with the simulation films to make sure the treatment is given to the right area. You may be asked to move your body to align yourself for treatment. Your oncologist will check your films before the radiation is given. This is standard practice to ensure the most accurate beam delivery. Once your films and position are confirmed the setup is done and the radiation can be given.

Your set-up appointment may be scheduled the day before you start radiation, or it may be scheduled along with your first day of radiation. This is based on the preference or availability of the facility where you are being treated.

Daily Treatments

Treatments are often given once a day, Monday through Friday, for a number of weeks. Sometimes, twice daily radiation treatments will be done. It takes about 5 minutes to get your radiation treatment, but you will likely be scheduled in a 25-30 minute appointment time. With set up and treatment you will be in the department for about an hour each day. This allows time for you to get changed, do any preparation, be positioned on the treatment table, receive your treatment, and for the therapists to clean all the equipment and setup the room of the next patient. Some factors that may affect the total time of your treatment include:

  • The number of treatment fields.
  • The type of imaging that is being used for your setup.
  • How long it takes to position you for treatment.

Each day, the therapists will position you on the treatment table, using the tattoos, immobilization devices, and laser beams on the machine to get you in the exact same position. The therapists will leave the room while giving the radiation to avoid exposure. They will be able to see and hear you from a control room just outside the treatment room. They can also give you instructions over a microphone as needed during the treatment. As you lie on the treatment table, the table and gantry may move to get the proton beams in the correct location. The treatment is not painful, and you will not feel anything during treatment.

Imaging is done daily prior to treatment to make sure you are in the best position possible for treatment. Additional imaging may be done weekly to see if plan changes are needed. If it is determined that changes are necessary for your plan, then imaging will be done on the first day of the new plan. The images taken during your radiation treatments are not used to see if you are responding to the radiation. They are used to make sure that the position and treatment arrangement are correct.

In some cases, when aligning you for treatment, your position may not be the best. In these cases, the radiation therapists will talk with your oncologist about what to do. From time to time the treatment plan needs to be adjusted and treatment may need to be paused until a new plan can be created. This will require having a new simulation.

Radiation therapists monitoring the treatment of a patient from the control room.

Proton therapy treatment room and machine.

Another view of the proton therapy treatment room and machine.

Proton therapy treatment room with a "fixed beam" machine.

On-Treatment Visit

Your radiation oncologist will meet with you at least once a week. The visit will take place just before or after your treatment is given. These visits give your provider the chance to see how you are doing, answer any questions you have, and plan future treatments.

If you are having a problem, you do not have to wait until your next on-treatment visit. Instead, you can ask to be seen or call the department. A provider will review your problem or concern and if they cannot help, they will contact your oncologist. If there are any problems at night or on weekends, call the hospital operator and ask for "the radiation oncologist-on-call."

End-Of-Treatment Visit

A day or two before your last treatment, you will have your final on-treatment visit with your provider. During this visit, they will talk to you about follow-up care and may do an exam.

Follow-Up Care

Follow-up appointments are often scheduled at 4 and 12 weeks after your radiation treatments are done. You may be asked to have a scan (CT, PET, or MRI) before this visit. Your provider will see how you are doing and give you information on continued follow-up care. It is important to go to your follow-up care appointments so that any radiation-related problems can be treated early. Your providers will also continue to consult with your other cancer specialists.

Resources for More Information

Preparing for Radiation: Simulation and Treatment


December 12, 2023

Holiday Lights Are My Favorite Thing

by Courtney Misher, MPH, BSRT(T)

June 9, 2022

Five Questions With…Michele.

by OncoLink Team

April 14, 2022

Five Questions with…Fred.

by OncoLink Team