CT simulation process in radiation therapy

Before you start radiation treatments, you will be scheduled for a CT scan called a Simulation in the Radiation Oncology department. This scan helps your care team map out exactly where the radiation should go and what areas to avoid.

During the scan, the Radiation Therapist will ask you to lie very still in the same position you’ll be in for your actual radiation therapy treatments.

Simulation steps

Step 1: Immobilization devices

To ensure each treatment is delivered accurately, the Radiation Therapists may create custom immobilization devices, depending on your treatment area and needs to help you stay in the same position every day:

• Masks - Used for patients receiving treatment to the head, neck, brain, or scalp. These are custom fitted to ensure consistent positioning.
• Vacuum bags (Vac-Lok) - Cushions that are shaped to your body and then firm up to hold you in place.

Step 2: Scanning

Once you're positioned, the Radiation Therapist will perform a CT scan. This scan provides detailed images that help your care team plan your radiation therapy.

Step 3: Alignment marks

To help align you consistently for each treatment:

• Small permanent marks (similar to freckles or dots) may be placed on your skin — except for patients receiving treatment to the head, neck or brain.
• These marks serve as reference points to ensure accurate daily positioning.
• They are essential for treatment precision and consistency.

Step 4: Documentation

Once the CT scan is complete, the Radiation Therapist will take photographs using a digital camera. These images are stored in your electronic health record and help guide your care team throughout your treatment.

To ensure accurate documentation of your alignment and skin marks, the treatment area will be uncovered during these photographs. This allows the care team to clearly see and record the reference marks and positioning used for your daily treatments.

Summary

The CT simulation serves as both a rehearsal and a blueprint for your radiation therapy.

• Immobilization devices keep you in the same spot.
• Skin marks act as a roadmap.
• The CT scan provides the detailed map your doctors need to guide your treatment with precision.

Tips for your appointment

• Wear comfortable clothing and shoes that are easy to remove.
• If you're receiving treatment to the chest or abdomen, you’ll be asked to wear a gown and remove all clothing from the waist up.
• For pelvic area treatments, gown pants will be provided if you're wearing tight fitted pants (ex: Jeans).
• Avoid wearing a belt or jewelry in the area being scanned or treated. It's best to leave them at home.
• The treatment area will need to be uncovered during simulation and daily treatments to ensure accuracy.

Special instructions

If your Radiation Oncologist orders specific preparation for your simulation, our care team will contact you with instructions. You may be asked to:

• Fill or empty your bladder.
• Empty your bowels.
• Practice breathing techniques or holding your breath.
• Practice holding still with your arms above your head.