# Bladder filling and rectal preparation for prostate radiotherapy

Source: https://onco.cc/protocols/prostate-radiotherapy-bladder-and-rectal-preparation/  
OnCo record `prostate-radiotherapy-bladder-and-rectal-preparation` (Protocol). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

For prostate radiotherapy you are usually asked to empty your bladder and then drink a set amount of water before the planning scan and every treatment. A comfortably full bladder pushes the bowel away from the radiation. Some centres also ask for a small enema or laxatives to empty the back passage, but newer studies suggest this is not needed for everyone when daily scans check the position.

## Summary

No guideline grades bladder or rectal preparation for prostate radiotherapy, and practice varies. Bladder: a comfortably full bladder lifts small bowel out of the pelvis and lowers bowel dose, but drinking protocols give inconsistent volumes from day to day (Nasser 2021 review). In a randomised trial of 110 men, 540 ml of water gave more reproducible bladder volumes than 1080 ml (median variation 76 against 105 ml) with no more toxicity; a 2021 meta-analysis of 11 studies (417 patients) found 300 to 400 ml gave the best reproducibility and that reproducibility fell as the volume rose. Checking the bladder on imaging before each fraction is the practical safeguard.

Rectum: a 2014 systematic review of 18 studies found no robust evidence for one rectal emptying method over another; randomised trials of simethicone (SPoRT, 30 men) and an antiflatulent (78 men) found no reduction in rectal volume or rescans; a small trial found an osmotic laxative gave less rectal gas than a bulking laxative with probiotic. In 295 Royal Marsden patients with daily cone-beam CT, micro-enema preparation reduced the share with a large rectum on the planning CT by only 10 to 15% and did not change intrafraction motion; the authors conclude preparation is not universally needed and recommend intervention where a large rectum coincides with seminal vesicle involvement or risk. A published comment reads the same data as support for risk-adapted, not universal, omission. The ESTRO ACROP IGRT guideline (2019) is cited by Alexander et al. as not recommending routine preparation; its full text could not be read.

## Fields

- Kind: Protocol
- Last checked: 2026-11-11
- Also known as: bladder filling protocol; full bladder for radiotherapy; drinking water before radiotherapy; rectal preparation for radiotherapy; micro-enema before radiotherapy; bowel preparation for prostate radiotherapy; empty bowel radiotherapy; bladder scan before radiotherapy

## Connected records

- cancers: [Prostate cancer](https://onco.cc/cancers/prostate/)
- technologies: [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [In-room imaging for radiotherapy (cone-beam CT, ExacTrac, CT-on-rails, HyperSight)](https://onco.cc/technologies/in-room-imaging-systems/)
- terms: [How many radiotherapy visits: the prostate fractionation trials](https://onco.cc/terms/prostate-radiotherapy-fractionation/), [Radiotherapy](https://onco.cc/terms/radiotherapy/)
- ideas: [A measured drink of water before pelvic radiotherapy, and bowel preparation kept to what trials support](https://onco.cc/ideas/idea-pu-pelvic-filling-protocol/), [An absorbable gel or balloon between prostate and rectum before radiotherapy, used under audit](https://onco.cc/ideas/idea-pu-rectal-spacer-prostate/)
- protocols: [Radiation precautions at home after permanent prostate seed brachytherapy](https://onco.cc/protocols/permanent-prostate-seed-brachytherapy-home-radiation-safety/), [Radiotherapy dose and fractionation by cancer site: UK reference schedules](https://onco.cc/protocols/radiotherapy-dose-fractionation-reference/), [Radiotherapy planning scan (CT simulation): positioning, skin marks and what the patient does](https://onco.cc/protocols/radiotherapy-planning-ct-simulation/)

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