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Radiation Therapy · Planning & Daily Logistics
Radiation Simulation (Planning CT) — What Actually Happens on Day One
Medically reviewed by Dr. Kirti Ranjan Mohanty, Radiation Oncologist, MBBS · MD (Radiation Oncology), Senior Consultant · Last reviewed August 2026
Your planning CT — also called simulation — is a mapping visit, not a treatment session, and no radiation dose is delivered that day. Most appointments run under an hour, following a sequence patient-education materials from bodies like NCCN and ASTRO describe consistently, yet nobody usually walks patients through it beforehand. Here's exactly what to expect, step by step.
- It's mapping, not treatment — no radiation dose is delivered at simulation; the visit maps your treatment area for later sessions.
- Usually one visit, under an hour — most planning CT appointments run 30-60 minutes from check-in to walking out.
- Contrast only if your plan needs it — whether contrast is used depends on your treatment site; your team tells you beforehand.
- Delivered at an NABH-accredited partner centre — CION coordinates your treatment plan, your oncology team and your care throughout.
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The short answer
What happens at a radiation planning CT (simulation) appointment?
A planning CT — also called simulation — is a single visit where a CT scan maps your treatment area and, if needed, a positioning aid is made so every future session lines up the same way. No radiation treatment is given that day; this visit is purely for planning.
Your radiotherapy itself is delivered at an NABH-accredited partner centre; CION Cancer Clinics coordinates your treatment plan, your oncology team and your care throughout, including this first planning visit.
The sections below cover exactly how long it takes, whether contrast is used, and why treatment doesn't start the same day.
Did you know?
Patient-education materials from bodies like NCCN describe the planning CT as the step where your care team turns an imaging scan into a precise, personalised treatment map — it typically happens only once per course, even if your treatment itself runs for several weeks.
Planning your day
How long does a radiation planning CT (simulation) take?
Most planning CT appointments take 30-60 minutes from check-in to walking out. The scan itself is quick, usually just a few minutes; most of the visit is spent on consultation, positioning and, for some treatment sites, making a mask or mould.
Build the full hour into your schedule rather than the scan time alone — this is the number to plan your commute, a half-day off work, or a companion's wait around, not the few minutes the CT itself takes.
Travelling in from outside Hyderabad for this visit? See our guide on daily travel from a district town for radiation in Hyderabad to help plan around it.
Nobody explains this beforehand
Your planning CT visit at a glance
A general pattern described in patient-education materials, not a forecast for your exact appointment. Ask your care coordinator for a specific estimate.
| Visit segment | Typical time | What's happening |
|---|---|---|
| Check-in & consultation | 10-15 minutes | Confirming details, answering questions, changing if needed |
| Positioning & mask/mould-making (if needed) | 10-20 minutes | Aligning you precisely; making a custom positioning aid for some sites |
| The planning CT scan itself | 5-10 minutes | The actual imaging that maps your treatment area |
| Marking & wrap-up | 5-10 minutes | Small reference marks placed; final questions answered |
Total: roughly 30-60 minutes for most patients. Actual timing depends on your treatment site and whether a positioning aid is needed — never guaranteed to the minute.
A common worry, answered directly
Is contrast given during a radiation planning CT?
Sometimes — whether contrast is used depends entirely on your treatment site and what your radiation oncology team needs to see clearly on the scan. Some sites are scanned without any contrast; others may need an oral or intravenous contrast agent to outline organs near the treatment area accurately.
This is decided as part of your treatment plan, not left to guesswork on the day — your team will tell you in advance if contrast applies to you, along with any preparation it needs, such as fasting beforehand.
If contrast is planned for your visit, ask your care coordinator exactly what preparation it needs so day one goes smoothly.
Setting expectations
Is radiation treatment given on the same day as simulation?
No. Simulation is a planning-only visit, and no radiation dose is delivered that day. Your planning CT scan is sent to a dosimetry team, who calculate the exact dose and beam angles for your case — a step that takes time and cannot be rushed for safety.
This means there is always a gap between your planning CT and your first actual treatment session, usually a few days, while your plan is calculated, checked and approved. That gap is normal and expected, not a delay in your care.
Curious exactly how long that gap runs and why? See Why Is There a Gap Between Planning and Your First Session? for the full explanation.
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Know exactly what to expect on day one
A radiation oncology team can walk you through your specific site, positioning and timing before you ever step into the planning room.
Walking through day one
What happens minute-by-minute at your planning CT appointment?
The exact sequence nobody explains beforehand — here's what to expect, step by step.
1
Check-in and paperwork
You arrive at your scheduled slot, check in, and confirm your details. No fasting is usually needed unless your team has told you contrast requires it.
2
A short consultation
A member of your radiation oncology team reviews your treatment plan with you and answers any last questions before you're taken in.
3
Positioning on the CT table
You're helped into the exact position you'll be treated in — lying still on a CT table, sometimes with simple supports to help you stay comfortable and steady.
4
Mask or mould-making, if your site needs it
For some treatment sites, such as head and neck, a custom thermoplastic mask or mould is made at this visit so you're positioned identically at every future session.
5
The planning CT scan
The CT scanner takes images of the treatment area — this is imaging only, not treatment, and takes just a few minutes.
6
Marking and wrap-up
Small reference marks, or marks on your mask, are placed to help line you up each day, then you're free to change and go home the same day.
Did you know?
The mask or mould made at simulation, if your treatment site needs one, is kept and reused at every session of your course — it is made once, on day one, specifically so your positioning never has to be re-measured from scratch.
What to expect for your treatment site
Does simulation look different depending on where you're being treated?
The overall sequence above is the same for everyone — a few details change depending on your treatment site.
Head & neck
A thermoplastic mask is standard
A custom mesh mask is moulded to your face and shoulders at simulation and reused at every session — many patients worry about this beforehand more than they need to. Read what it actually feels like and how to cope.
Breast
A support board, not a mask
You're positioned on a simple angled board with your arm raised — no mask is needed for most breast treatment plans.
Pelvic sites
Bladder or bowel prep may apply
Some pelvic treatment plans ask for a specific bladder-filling or bowel-prep routine before simulation, so your internal anatomy sits consistently at every visit. See exactly what that involves.
Other sites
Simple positioning aids
Many other sites use a lightweight cushion or mould rather than a mask — your team will tell you in advance exactly what your own simulation involves.
Before you go
How to prepare for your radiation planning CT appointment
Practical steps that help most patients — and the family members accompanying them — walk in ready.
- Wear comfortable, easy-to-remove clothing — you may be asked to change, so clothing without metal fasteners near the treatment area is easiest.
- Bring your reports and referral letter — recent scans, biopsy results and your oncologist's referral help the team confirm your plan on the day.
- Ask about eating and fasting beforehand — most simulation visits need no fasting, but confirm this in advance if contrast is planned for your scan.
- Arrange a companion if you'd like one — there's no medical reason you must come alone; a family member is welcome to wait with you.
- Plan the full hour, not just the scan time — build 30-60 minutes into your schedule, including consultation and positioning, not only the few minutes of scanning.
- Write down your questions beforehand — this is the easiest time to ask about timing, contrast, or what a mask or mould involves; the team expects these questions.
Accompanying a parent to this visit? The same steps apply — arriving early, carrying their reports and asking questions on their behalf all help the visit go smoothly.
You don't have to walk in unprepared
One conversation can replace the guesswork
Whether you're the patient or accompanying a parent, a radiation oncology team can explain exactly what your planning CT day will look like.
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Common questions
Radiation planning CT (simulation) — your questions answered
How long does a radiation planning CT (simulation) take?
Most planning CT appointments take 30-60 minutes from check-in to walking out, though the CT scan itself is quick — usually just a few minutes. The rest of the visit is consultation, positioning, and, for some treatment sites, making a custom mask or mould. Build the full hour into your schedule, not just the scan time, when planning your commute or a half-day off work.
Is contrast given during a radiation planning CT?
Sometimes — it depends on your treatment site and what your radiation oncology team needs to see clearly on the scan. Some sites are imaged without any contrast; others may need an oral or intravenous contrast agent to outline nearby organs accurately. This is decided as part of your treatment plan in advance, and your team will tell you beforehand if it applies to you, along with any preparation such as fasting.
Is radiation treatment given on the same day as simulation?
No. Simulation is a planning-only visit, and no radiation dose is delivered that day. Your planning CT scan is sent to a dosimetry team, who calculate your exact dose and beam angles — a step that takes time and can't be rushed for safety. There's always a gap of a few days between simulation and your first actual treatment session while this planning work happens, and that gap is expected, not a delay.
Will I need a mask or mould made during simulation?
It depends on your treatment site. Head and neck treatment plans usually use a custom thermoplastic mask, moulded to your face and shoulders at simulation and reused at every session afterwards. Breast treatment typically uses a simple angled support board instead of a mask. Other sites may use a lightweight cushion or mould. Your team will tell you in advance exactly what your specific plan involves.
What should I wear or bring to my planning CT appointment?
Wear comfortable clothing that's easy to change out of, ideally without metal fasteners near your treatment area. Bring your recent scans, biopsy results and your oncologist's referral letter. Most simulation visits need no fasting, but confirm this in advance if contrast is planned for your scan. A family member or companion is welcome to come with you and wait during the appointment.
What happens after simulation, before my first radiation session?
Your planning CT images go to a dosimetry team, who calculate the precise radiation dose and beam angles for your case, and your plan is then checked before it's approved for treatment. This process typically takes a few days, which is why your first treatment session doesn't happen on the same day as simulation. For a full explanation of that gap and what happens during it, see our guide on the wait between planning and your first session.
This page explains, in general terms, what typically happens during a radiation planning CT (simulation) appointment; it is not a substitute for guidance from your own oncology team about your specific diagnosis, site and treatment plan.