Treatment Planning for Proton Therapy
You and your Indiana University Health Proton Therapy Center team begin planning your treatment after you’ve finalized your decision and your health insurance provider has approved your care. Every patient’s proton therapy plan is different, even if two people have the same type of cancer. We work closely with you to customize your care. Treatment planning takes from two to four weeks, depending on the complexity and urgency of your case.
The period before you start treatment is a good time to explore your housing options, make travel arrangements and arrange other personal matters.
You may need to have a preliminary set of computed tomography (CT) and magnetic resonance imaging (MRI) scans before we plan your treatment. This is most likely if you have a neurologically based tumor or a complex case.
Sometimes, we need to place special positioning markers in patients. These markers help in treatment planning and with daily positioning for treatments. Fiducial markers are surgically implanted during an outpatient procedure at another facility. Our staff members schedule and coordinate these appointments for you.
Fiducial markers help the proton therapy team to see tumors and accurately position you for treatment.
The list below outlines the types fiducial markers that are used for proton therapy and the facilities that we use for these procedures.
- Dental, skull and spine fiducials: Appointments are scheduled with one of the following groups:
- Prostate seed markers: We commonly use IU Health Southern Indiana Physicians - Urology
- Some head and neck patients: We typically order one of the following:
- A dental bite block (created by an outside provider; selection is based on tumor type and location)
- A bite block (created onsite)
- A commercially made bite block
It is important for proton therapy patients to remain completely still during treatment sessions. We use immobilization devices to position patients, including face masks, body molds and mouthpieces. These devices are custom made for you.
For prostate cancer patients, we create a custom plastic device similar to a back brace that molds to your lower abdomen and pelvis that you are fitted into during proton therapy sessions to ensure your positioning is consistent each time.
Planning CT Scan
You have a planning computed tomography (CT) scan after your fiducial markers are in place and your immobilization devices are made. This CT scan must match the position we place you in for daily treatment. This scan helps to define the treatment area, location of implanted markers and other anatomical structures.
Most planning CT scans are completed at our facility.
If you are a prostate cancer patient, a rectal balloon will be inserted prior to the CT scan. The rectal balloon pushes the rectal wall down and pushes the bladder up to support the prostate in position to reduce movement. This process helps us reduce the radiation dose to surrounding organs.
Developing Your Treatment Prescription and Plan
Your physician views the data from the planning CT scan on a computer to outline the area to be treated with proton therapy and identify important structures to avoid. The physician writes a dose prescription for the treatment with limiting doses for other structures. For the majority of our prostate patients, the dose prescription is 44 treatments. For other conditions, the number of treatments is dependent on your case.
Our dosimetry (dose planning) team uses the physician’s dose prescription to create a custom plan to deliver the proton beams from different directions to maximize the dose to the treatment area and minimize the dose to structures. This plan includes the number of fields (angles, positions) the proton beam will be directed at you. Prostate patients tend to have two fields⎯one treatment from the left side and one from the right side. The fields for other treatment plans vary from one to six or more.
Your final treatment plan is reviewed and approved by your radiation oncologist.
Developing Beam-Shaping Devices
We shape the proton beams you will receive with custom-made shielding devices, made by the Indiana University Cyclotron Operations, called apertures and compensators. These devices shape the beams to the precise treatment area outlined in your treatment plan and block the proton beams from treating normal tissues.
- The aperture is a heavy solid brass cylinder with a specially designed opening to match the profile of the treatment area. The aperture is contoured to the exact shape of the target volume. The aperture shapes the proton beam up and down and left to right (X and Y axes). The beam cannot penetrate through the solid part of the brass and is only directed through the opening.
- The compensator is a custom acrylic mold that modifies the shape of the beam and contours the depth (Z axis) of the treatment area. The compensator’s center is carved out to match the prescribed dosage for proton delivery.
We create custom apertures and compensators for each field prescribed in your treatment plan.
Verification Simulation (V-Sim)
The final step before you begin treatment is your Verification Simulation (V-Sim) appointment. This is the trial run to confirm planning, positioning and treatment devices, and it usually occurs a day or two before you start treatment.
A radiation therapist (staff member who administers the treatments) or a therapy assistant will bring you into the treatment room and position you in your custom immobilization devices. We verify your positioning in relation to the proton beam, confirm sizes of the beam-shaping devices and make sure you are as comfortable as possible in your immobilization device. We rehearse every step in your treatment except for beam delivery.
Your V-Sim appointment lasts 30 to 60 minutes. You usually start treatment within two days afterward. If your V-Sim appointment revealed necessary modifications to your treatment plan, your therapy start date may be delayed.