# Radiotherapy planning scan (CT simulation): positioning, skin marks and what the patient does

Source: https://onco.cc/protocols/radiotherapy-planning-ct-simulation/  
OnCo record `radiotherapy-planning-ct-simulation` (Protocol). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Before radiotherapy starts you have a planning appointment, usually a CT scan. You lie in the exact treatment position, sometimes with a mask, mould or cushion, and keep very still. Small skin marks (permanent dots or temporary ink) may be made to line you up each day. Depending on the area, you may need a full or empty bladder, a dye injection, or breath-hold practice.

## Summary

The NCI booklet (2021) describes the planning session for patients: the radiation oncologist and therapist define the treatment area while the patient lies very still for scans; small permanent tattoos or ink dots are placed to line the patient up daily; a body mould or, for the head and neck, a mask may be made. The ESTRO ACROP head and neck guideline (2017) gives the radiographer's procedure: identification and consent checked before scanning; diagnosis, prescription and scan margins known in advance to keep imaging dose as low as reasonably achievable; contrast screened for, kidney function checked and the patient observed for at least 15 minutes after; nodes and scars marked and bolus placed before scanning; the couch set so all immobilisation is in the field of view; orientation entered correctly; slice thickness of 3 mm or less; dose-length product recorded; a photograph of the set-up taken if needed.

On skin marks, ESTRO-ACROP breast (2023) reports a randomised trial (176 against 166 patients) with no difference in set-up error between permanent tattoos and temporary marks on weekly portal imaging, notes that tattoos may affect wellbeing, and considers that surface guidance may allow marks to be omitted if validated locally. A randomised trial in 196 women found that a virtual-reality explanation before breast radiotherapy planning reduced anxiety immediately and improved knowledge of the procedure compared with the standard explanation. Site-specific preparation (bladder and bowel filling, breath-hold, 4D CT, masks) is in linked protocols.

## Fields

- Kind: Protocol
- Last checked: 2026-11-11
- Also known as: CT simulation; CT sim; planning CT; radiotherapy planning appointment; simulation; virtual simulation; radiotherapy tattoos; reference marks; mould room

## Connected records

- protocols: [Bladder filling and rectal preparation for prostate radiotherapy](https://onco.cc/protocols/prostate-radiotherapy-bladder-and-rectal-preparation/), [Breast radiotherapy positioning, immobilisation and daily set-up verification](https://onco.cc/protocols/breast-radiotherapy-positioning-and-setup/), [Breathing motion in lung and upper abdominal radiotherapy: 4D CT, gating, breath-hold and compression](https://onco.cc/protocols/respiratory-motion-management-4d-ct-and-gating/), [Deep inspiration breath-hold for left-sided breast radiotherapy](https://onco.cc/protocols/breath-hold-left-breast-radiotherapy/), [Immobilisation mask for head and neck and brain radiotherapy, including mask anxiety](https://onco.cc/protocols/head-and-neck-radiotherapy-immobilisation-mask/), [Iodinated contrast for CT: kidney function checks, kidney protection and metformin](https://onco.cc/protocols/iodinated-contrast-kidney-and-metformin/), [Patient identification and pre-treatment time-out in radiotherapy](https://onco.cc/protocols/radiotherapy-patient-identification-and-time-out/), [Pregnancy and breastfeeding checks before radiotherapy](https://onco.cc/protocols/radiotherapy-pregnancy-and-breastfeeding-enquiry/)
- cancers: [Breast cancer (all types)](https://onco.cc/cancers/breast-cancer/), [Head and neck squamous cell carcinoma](https://onco.cc/cancers/head-and-neck/)
- technologies: [CT (computed tomography)](https://onco.cc/technologies/ct/), [Iodinated and barium contrast for CT and X-ray](https://onco.cc/technologies/iodinated-contrast-media/), [Radiotherapy treatment planning and QA software](https://onco.cc/technologies/treatment-planning-systems/), [Respiratory motion management (4D-CT, gating, breath-hold, tracking)](https://onco.cc/technologies/respiratory-motion-management/), [Surface-guided radiotherapy (SGRT)](https://onco.cc/technologies/surface-guided-radiotherapy/)
- terms: [Radiotherapy](https://onco.cc/terms/radiotherapy/)
- ideas: [Radiotherapy set-up without permanent ink tattoos, using surface guidance or invisible ink](https://onco.cc/ideas/idea-pu-tattoo-free-set-up/), [Show people the radiotherapy room and the treatment before the planning appointment, using virtual reality or a guided visit](https://onco.cc/ideas/idea-pu-radiotherapy-walkthrough-before-planning/)

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