The short answer
Radiation simulation is the planning appointment that maps exactly where your radiation will go. You'll usually lie on a table while a CT scan is taken in your treatment position; the team may make small skin marks (sometimes tiny permanent dots) or a custom mold to keep you still and precise. It's painless, takes roughly 30–60 minutes, and no radiation treatment is given that day.
Simulation is a planning session, not a treatment — no radiation is delivered.
A CT scan in your treatment position maps where radiation should go.
Small skin marks or a custom mold help line you up precisely each time.
It's painless and usually takes about 30–60 minutes.
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The full explanation.
The short answer
Radiation simulation is the planning appointment that maps exactly where your treatment will be aimed. You lie in your treatment position while a CT scan is taken; the team may add small skin marks or a custom mold so you can be lined up precisely each time. It's painless, takes about 30–60 minutes, and no radiation is given that day.
Before the visit
Wear comfortable, easy-to-change clothing. Ask ahead whether to avoid lotions or deodorant, and whether anything else applies to the area being treated.
What commonly happens
- You lie on a table in the position you'll be in for treatment.
- A CT scan (and sometimes other imaging) maps the area.
- The team may make small skin marks — temporary or tiny permanent dots — to guide alignment.
- For some areas, a custom mold or mask is made to help you stay still.
How long it takes
Usually about 30 to 60 minutes, most of it spent getting the position exactly right.
Why it matters
Precision is the point. The care you feel during simulation is what lets the daily treatments target the cancer while sparing healthy tissue.
What happens afterward
The team uses your scan to design the treatment plan, which takes some days. Ask when your first actual treatment session will be.
Words to know
Tap any term to see what it means.
Common questions
▸Does simulation hurt?
No. It mainly involves lying still while a scan is done. The hardest part for some people is holding the position, which is why molds or supports are used to help.
▸Are the skin marks permanent?
Sometimes. Some centers use tiny permanent dots (like small tattoos) for accuracy; others use temporary marks. Ask your team which they use so you know what to expect.
Questions to ask your doctor
Being prepared helps you get the most out of your appointments. Save or print these questions.
Tap a question to save it to your list (kept on this device).
Your next step
Get ready with a checklist and questions for the visit.
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