Under physician review

Handout: Your CT Simulation Session

Radiotherapy Step by Step — Designed for radiation oncologists to use in clinic

Before your treatment starts, we need a precise "map" of your body in the exact treatment position. This session is for imaging and preparation only — no treatment is given.

What happens in this session?

You will lie on the CT couch in the same position you will be treated in later, and the therapists will help you settle comfortably using cushions and purpose-made immobilization devices.
The session usually takes 15–45 minutes, mostly for positioning; the scan itself takes only a few painless minutes.
In some cases intravenous contrast dye is used to clarify the images — tell the team if you have had an allergy before or have kidney problems.

Skin marks

At the end of the session the therapists place small marks on your skin — tiny freckle-sized tattoo dots, or special pen marks with clear stickers — used to align your body precisely at every session.
Protect these marks: do not scrub or remove them when washing, and tell the team immediately if they fade or come off.

Immobilization: why staying still matters

Treatment accuracy depends on you being in the same position to the millimeter at every session. We therefore use aids such as molds, vacuum cushions, and positioning boards.
For head or neck treatment, a custom mesh mask is made from a material softened in warm water and shaped to your features within minutes — the mask is perforated and you can breathe through it completely freely.
If you feel uneasy in enclosed spaces or with the mask, tell us early — we have many ways to help you feel comfortable.

What will you feel? Who is with you?

The session is completely painless. The most you may notice is a cool room (needed for the equipment) or the length of time lying still.
The team sees and hears you the whole time via cameras and an intercom, and the session can be paused at any moment if you need it.