Radiotherapy planning CT scan

A special CT scan, taken in your treatment position, that maps exactly where the cancer and nearby organs are so your radiotherapy team can plan precisely where the radiation will go. It is a planning step, not the treatment itself.

✓ Medically reviewed by a GMC-registered consultant · last reviewed September 2026 · next review September 2027 · how we review

In short

It is a planning scan that maps where the cancer and nearby organs are, so your radiotherapy can be aimed precisely — it is not the treatment itself.
You may have a mask or mould made and tiny reference marks or permanent pinpoint tattoos to line you up the same way each time.
There is no result to receive; the scan is used to design your plan, which is usually ready a few days to about three weeks before treatment starts.
It is quick and you feel nothing from the scan, though you may need contrast or a bladder/bowel preparation for some areas.

A plain-English summary. The detail — including risks and recovery — is below.

At a glance

TypeA planning scan (imaging) used to design radiotherapy — not the treatment

AnaestheticNot needed for adults; young children may occasionally need sedation or anaesthetic to keep still

How long it takesOften 15 minutes to about an hour, including positioning and any mask or mould

Hospital stayOutpatient — you go home the same day

Time off workUsually none for the scan itself, beyond the appointment time

When you'll see resultsThere is no result to receive; the scan is used to design your treatment plan, which is ready before treatment starts (often a few days to about 3 weeks later)

On the NHS?A standard part of NHS radiotherapy; private care is mainly used for speed or choice and is coordinated with your cancer team

A general guide. Your radiologist will give you advice for your situation.

Best fit

Lets the team see exactly where the cancer and nearby organs are, in your treatment position

Pause if

Radiotherapy is not the right treatment for your situation, so a planning scan is not needed.

Main recovery point

You lie still while you are positioned, any mask or mould is made, and the scan is taken. You feel nothing from the scan itself.

Good aftercare

A clear explanation that this is planning, with the date treatment will start.

During the appointment

You lie still while you are positioned, any mask or mould is made, and the scan is taken. You feel nothing from...

Straight afterwards

You can usually go home and carry on as normal. If you had a contrast injection, you may be asked to wait a short...

Over the following days

The clinical oncologist, physicists and dosimetrists use the scan to design and check your treatment plan.

Before treatment starts

Your radiotherapy usually begins a few days to about three weeks later, once the plan is ready and checked.

Medical line illustration of radiotherapy treatment for Radiotherapy planning CT scan. — Illustration only - not a diagnosis, medical advice or a promise of result. Your anatomy and treatment plan may differ. Vuemedics does not publish before-and-after photos.

What is a radiotherapy planning CT scan?

A radiotherapy planning CT scan (also called CT simulation) is a special scan taken to design your radiotherapy. You lie in the exact position you will be in for treatment, and the scan maps where the cancer and the healthy organs around it are.

It is not a diagnostic scan to find or stage cancer, and it is not the treatment. Its job is to give your radiotherapy team — clinical oncologists, physicists and radiographers — the detailed picture they need to plan precisely where the radiation beams will go and which areas to protect.

During the appointment the team may make a mask, mould or other support so you stay in the same position for every treatment, and may make tiny reference marks or permanent pinpoint tattoos on your skin to line you up accurately. For some areas you may need a contrast injection or a bladder or bowel preparation so structures show up clearly.

After the scan, the team uses it to build your treatment plan over the following days. The scan itself involves a small dose of radiation, but the careful planning it allows is what makes your treatment accurate.

Types, options & approaches

There may be different ways to do this. The right approach depends on the clinical question and your circumstances.

Planning scan with an immobilisation mask

For treatment to the head, neck or brain, a close-fitting plastic mask is made to keep you very still. It is moulded to your face and hardens in a few minutes; it can feel snug but you can breathe through it.

Planning scan with body supports or moulds

For other areas, supports such as a chest board, headrest, arm pole or leg or foot supports help you lie in the same comfortable, repeatable position each time.

Planning scan with contrast

Sometimes a contrast injection (or a drink) is used to make blood vessels or other structures show up, so the team can see the area more clearly.

Planning scan with bladder or bowel preparation

For pelvic treatment you may be asked to have a comfortably full or empty bladder, or to follow bowel advice, so the organs sit in a consistent position.

Four-dimensional (4D) planning scan

For areas that move with breathing, such as the chest, the scan can capture movement over the breathing cycle so the plan allows for it.

Planning CT scan compared with a diagnostic CT scan

Feature	Planning CT scan	Diagnostic CT scan
Purpose	To design radiotherapy	To find, stage or check on disease
Position	Your exact treatment position	Whatever is best to see the area
Extras	Mask/mould, reference marks or tattoos	Usually none of these
Result	Used to build a plan, no report to you	A radiologist's report on the findings

A planning scan is about setting up accurate treatment, not about diagnosing disease, so you do not get a 'result' from it in the usual sense.

Preparing for your scan

Check whether you need to do anything beforehand, such as arriving with a full or empty bladder or following bowel advice for pelvic treatment.
Tell the team if you have a contrast allergy, kidney problems, diabetes medicines or are or might be pregnant, especially if contrast may be used.
Wear comfortable clothes; you may be asked to change into a gown and remove jewellery from the area.
Allow more time than a quick scan, as making a mask or mould and positioning you can take a while.
If you find enclosed spaces or masks difficult, tell the team in advance so they can support you.
Ask whether you will have permanent pinpoint tattoos or temporary marks, and what they are for.
Bring a list of your medicines and any questions about what happens next.

What happens

You come to the radiotherapy department as an outpatient. The radiographers position you on the scanner couch in the exact position you will be treated in, which needs to be comfortable enough to hold still and repeat each time.

If you need an immobilisation device, such as a mask for head or neck treatment or supports for other areas, this is made or fitted now. A mask is moulded to you and hardens within a few minutes; you can still breathe.

The CT scanner, a doughnut-shaped ring, then moves around you while you lie still. The scan itself takes only a few minutes and you do not feel anything. The team watches from the next room and can talk to you. For some areas you may have a contrast injection first.

Finally, the radiographers make small reference marks on your skin, often tiny permanent pinpoint tattoos, to line you up accurately for treatment. You then go home. There is no result on the day — the team uses the scan to design your plan over the following days before treatment begins.

Is this scan right for me?

A good consultation should explore whether it's the right choice for you now — including reasons to wait or consider something else.

May not be suitable if…

Radiotherapy is not the right treatment for your situation, so a planning scan is not needed.
You cannot lie still in the required position, even with support, and this has not yet been addressed.
A contrast scan is planned but contrast is unsafe for you, so the approach needs adjusting.
A decision on whether to proceed with radiotherapy has not yet been made.

Delay or rearrange if…

There is any chance of pregnancy, until this has been clarified.
You have an untreated contrast allergy or kidney concern that needs addressing first, if contrast is planned.
The treatment decision or target area has not yet been finalised by your team.
You are too unwell to lie still for the appointment and need support arranged first.

Alternatives to discuss

Planning based on other or additional imaging, such as MRI, matched to a CT, where appropriate.
Repeating or adjusting the planning scan if your anatomy changes.
Different immobilisation or positioning aids if you find the standard set-up difficult.
No radiotherapy, if a different treatment or approach is chosen.

Before you decide

Use this as a shared-decision checklist. The aim is not just “can this be done?”, but whether it is right for you, now, with the risks and alternatives clearly understood.

What matters most to me?

Think about symptoms, daily life, work, caring responsibilities, sport, fertility, travel, appearance and anxiety — the right choice depends on your priorities, not just the medical facts.

What are all my options?

Ask about waiting, monitoring, medicines, rehabilitation, a smaller or larger procedure, a different test, NHS referral, or a second opinion where that would help.

What would make me pause?

Active infection, pregnancy, unstable medical problems, smoking, medicines that increase bleeding, poor support at home, or feeling pressured are all reasons to slow down and get tailored advice.

What happens if I do nothing today?

For some problems, waiting is safe; for others, delay can make treatment harder. A good consultation should explain the trade-off in plain English.

Benefits

Lets the team see exactly where the cancer and nearby organs are, in your treatment position
Allows the radiation to be aimed precisely at the target while protecting healthy tissue
Helps make every treatment session line up the same way, improving accuracy
Identifies areas to avoid, which can reduce side effects
Is a quick, usually not painful appointment that you feel nothing from

Risks & complications

More common

A small dose of radiation from the CT scan itself
Having to lie still in one position for a while, which some people find uncomfortable
Mild anxiety from wearing a close-fitting mask, if one is needed
A tiny permanent pinpoint tattoo mark, if used, that stays on the skin

Less common

A reaction to contrast dye, if contrast is used (usually mild)
Needing the scan repeated if the position or images are not right
Discomfort from a full bladder or bowel preparation for pelvic treatment

Rare but serious

A more serious allergic reaction to contrast, which the team is trained to treat
Contrast affecting the kidneys in people who already have kidney problems

This is a low-risk planning step. The main things to mention to the team are any contrast allergy, kidney problems or chance of pregnancy, and any difficulty lying still or wearing a mask. The scan does not treat the cancer or tell you how the cancer will respond; it is there to make the actual treatment as accurate as possible.

Published figures to discuss

A planning CT scan is a low-risk imaging step. The radiation dose is small and the main uncertainties relate to contrast (if used) rather than the scan itself. Reliable single percentages for harm from a planning scan are not meaningful, and serious reactions are rare, so we describe the risks qualitatively rather than quote invented figures.

Figure	Reported range	How to interpret it	Source / confidence
Planning scan not being the same as a diagnostic CT	Expected	The scan is optimised for treatment planning and may not answer every diagnostic question.	Guide sourcesClinical context
Contrast reaction if IV contrast is used	Uncommon; severe reactions are rare	Previous contrast reaction, kidney disease and some medicines should be checked.	Guide sourcesClinical context
Set-up tattoos or marks being permanent	Common with traditional tiny tattoos; alternatives vary by centre	Ask before the scan if permanent marks are a concern.	Guide sourcesClinical context
Need for re-planning	Uncommon but recognised	Weight change, tumour shrinkage, poor mask fit or anatomy changes can mean another planning scan is safer.	Guide sourcesClinical context

These are literature figures, not a personalised prediction. Your own risks and likely benefits depend on your circumstances, your health, and how your care is carried out and followed up.

What happens afterwards

There is no physical recovery from a planning scan. You can usually go straight back to your normal day. The point of the appointment is to design your treatment, which the team prepares before your radiotherapy starts.

During the appointment

You lie still while you are positioned, any mask or mould is made, and the scan is taken. You feel nothing from the scan itself.

Straight afterwards

You can usually go home and carry on as normal. If you had a contrast injection, you may be asked to wait a short time first.

Over the following days

The clinical oncologist, physicists and dosimetrists use the scan to design and check your treatment plan.

Before treatment starts

Your radiotherapy usually begins a few days to about three weeks later, once the plan is ready and checked.

What's normal — and not a worry

No physical after-effects from the scan
Being able to return to normal activities the same day
A small permanent pinpoint tattoo mark, if one was used
A short wait before treatment starts while the plan is prepared
Mild relief or tiredness if you found the mask or positioning stressful

Aftercare

Carry on with normal activities unless the team advises otherwise.
If you had contrast, drink plenty of fluids afterwards as advised.
Look after any skin marks; do not scrub off temporary marks if asked to keep them.
Keep the appointment details for when your treatment is due to start.
Note any questions about your treatment plan to ask at your next appointment.
Contact the department if you were unwell after contrast or have concerns before treatment.

Before your scan

Any bladder or bowel preparation instructions understood for future treatment
Contrast allergy, kidney issues or pregnancy possibility mentioned to the team
Comfortable clothing for the appointment
Extra time allowed for positioning and mask or mould making
Date and details of when treatment starts noted
Contact number for the radiotherapy department saved

⚠ Get urgent help if…

Breathing difficulty, swelling of the face or lips, or a widespread rash after a contrast injection — seek help immediately
Feeling faint, very itchy or unwell shortly after contrast
A reaction at the injection site that is spreading or very painful
Reduced urine or feeling very unwell in the days after contrast, especially with existing kidney problems
Anything the team specifically asked you to report after contrast

Who to contact: your clinician, clinic or test provider first (keep their number to hand). For urgent advice when you can't reach them, call NHS 111. In an emergency, call 999.

General guidance — it doesn't replace the specific advice your radiologist gives you.

Results & realistic expectations

A planning CT scan does not give you a result in the usual sense. It is not used to diagnose or stage the cancer or to judge how it will respond. Instead, the images are used by your radiotherapy team to design exactly where the radiation will go and which areas to protect.

The outcome you should expect is a carefully prepared treatment plan, ready before your radiotherapy begins. If you want to understand your diagnosis, staging or likely outcome, that comes from your oncology consultations and diagnostic scans, not from the planning scan.

How long it lasts

A planning scan reflects your anatomy at one point in time. If there is a long gap before treatment, or if your body changes (for example significant weight change, or a tumour shrinking during treatment), the team may repeat the scan and re-plan so treatment stays accurate. Reference marks or tattoos are used to keep your set-up consistent throughout the course.

Related tests, treatments or support

The planning scan is one step in a wider radiotherapy pathway. It may be combined with other imaging, such as MRI or PET, that is matched to the planning CT to outline the target more precisely. It is closely linked to the treatment that follows and to the daily position checks (image guidance) done at each session.

Follow-up & long-term care

There is no separate result appointment for the scan itself. The next step is the start of your radiotherapy once the plan is ready, usually within a few days to about three weeks. Your oncology team coordinates this, and any private planning should be joined up with your wider cancer care and GP.

Repeat, follow-on and what comes next

The scan may be repeated if the position or images are not adequate.
Re-planning and a new scan may be needed if your body changes during the course (for example weight change or tumour shrinkage).
The plan is checked and may be adjusted before treatment to keep it accurate.

Ask what happens if the result is unclear or needs repeating, and what is included if further tests or follow-up are needed.

What good aftercare looks like

A clear explanation that this is planning, with the date treatment will start.
Written instructions on any bladder, bowel or contrast preparation for future sessions.
A named contact for questions before treatment begins.
Joined-up care between any private provider, your NHS oncology team and your GP.
Re-planning offered promptly if your anatomy changes during treatment.

What affects the cost

Costs vary a great deal between people and providers, and we don't publish prices. What matters is understanding what drives the cost and making sure your quote is complete. The main things that affect it:

Whether the scan is part of a wider private radiotherapy package
The radiographers', physicists' and oncologist's planning time
Whether contrast is used
Whether an immobilisation mask or mould is needed
Any additional imaging (such as MRI or PET) matched to the planning scan

Make sure your written quote includes

Whether the planning scan is included in the overall radiotherapy cost
The facility and staff fees for planning
Contrast and immobilisation device costs, if relevant
Any extra imaging matched to the planning scan
What happens, and what it costs, if the scan needs repeating
How the planning links to the cost of the treatment course itself

On the NHS? A radiotherapy planning CT scan is a standard part of NHS radiotherapy; private care is mainly used for speed or choice of provider and should be coordinated with your cancer team.

You're entitled to your total cost in writing — including reports, follow-up and what happens if the result is inconclusive — before you decide.

Choosing a specialist safely

Check the radiologist is on the GMC Specialist Register for this area.
Make sure they work at a CQC-registered service, and look for membership of the relevant Royal College or professional body.
You're entitled to time to consider and to have your questions answered before you agree — the radiologist who looks after you should explain it, not a salesperson.
Be wary of pressure: time-limited offers or deposits taken before you've had time to think are red flags, not bargains.
You're entitled to your total cost in writing — including any follow-up — before you decide.

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Questions to ask your medical professional

Take this to your consultation. A good radiologist will welcome every one of these.

Will I need a mask, mould or other support, and what will that feel like?
Will my skin marks be permanent tattoos or temporary, and why?
Do I need contrast, a full bladder or any bowel preparation for my scan?
How long after this scan will my radiotherapy start?
Might the scan need repeating during treatment, and what would that mean?
Who do I contact if I have problems before treatment begins?
Are you on the GMC Specialist Register for this area, and which Royal College or professional body are you a member of?
Will you be the radiologist who carries out my scan, and who looks after me afterwards?
What are the risks for someone like me, and how often do your own patients have a problem or need it repeated or redone?
What does a realistic result look like — and what can this scan not achieve?
What are my options, including waiting, doing nothing for now, or choosing a different approach?
Can I have written information, results and aftercare instructions in a format I can use, including any accessibility or communication support I need?
What is the total cost in writing, including any follow-ups, and how much time do I have to decide?

Frequently asked questions

Is the planning CT scan the same as my radiotherapy treatment?

No. It is a planning step to map where the cancer and nearby organs are, so your treatment can be aimed accurately. The treatment itself comes later, once the plan is ready.

Will I get the results of the planning scan?

Not in the usual sense. The scan is used to design your treatment, not to diagnose or stage the cancer. Your diagnosis and outlook are discussed in your oncology consultations, not from this scan.

Do the tattoo marks have to be permanent?

Often tiny permanent pinpoint tattoos are used so you can be lined up the same way at every session. Ask your team whether permanent or temporary marks will be used and why.

Does the scan hurt or feel strange?

You do not feel the scan itself. Lying still for a while, wearing a close-fitting mask if one is needed, or having a full bladder for pelvic treatment can feel uncomfortable, but the team will help you.

Why might I need contrast dye?

Contrast helps certain structures, such as blood vessels, show up clearly so the team can plan more accurately. Tell them about any allergy, kidney problems or chance of pregnancy beforehand.

How long until my treatment starts?

Treatment usually begins a few days to about three weeks after the planning scan, once the team has designed and checked your plan.

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How we made this page

Medically reviewed by a GMC-registered consultant. Written in plain English, checked against NHS, NICE, GMC and relevant Royal College / specialist-society guidance, and kept under review. No clinic paid to appear on this page, and we publish no pricing. This is general information to help you prepare — it is not a substitute for advice from your own clinician. How we review our guides →

Source hierarchy: UK regulator and NHS/NICE guidance first, then relevant Royal College or specialist-society guidance, then peer-reviewed evidence for procedure-specific figures where available.

Sources & standards: Cancer Research UK — Planning your external radiotherapy Cancer Research UK — Radiotherapy moulds and masks Cancer Research UK — Creating your radiotherapy plan NHS — Radiotherapy Royal College of Radiologists — Clinical oncology

Reviews reflect patients' experience of care, not clinical outcomes. For procedure volumes and outcome data see PHIN.

Last medically reviewed 2026-09-21. Spotted something wrong or out of date? Report an error in this guide.