# An absorbable gel or balloon between prostate and rectum before radiotherapy, used under audit

Source: https://onco.cc/ideas/idea-pu-rectal-spacer-prostate/  
OnCo record `idea-pu-rectal-spacer-prostate` (Idea). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

A spacer injected between the prostate and the rectum pushes the bowel out of the high-dose area for a few months and then dissolves. Randomised trials found fewer bowel side effects, but the procedure carries its own rare serious complications, and England's guidance allows it only with special arrangements for consent and audit.

## Summary

What it is. Before prostate radiotherapy, a hydrogel, hyaluronic acid or a biodegradable balloon is placed through the skin between the prostate and the rectum under ultrasound, creating a gap of about a centimetre that lasts through treatment and is absorbed afterwards.

The randomised evidence. In the pivotal hydrogel trial, 222 men having 79.2 Gy in 44 fractions were randomised to spacer or none. The spacer created 12.6 millimetres of separation against 1.6 in controls, cut the rectal volume receiving 70 Gy from 12.4 to 3.3 per cent, and late rectal toxicity at 3 to 15 months was 2.0 against 7.0 per cent; 11.6 against 21.4 per cent of men had a meaningful decline in bowel quality of life at 15 months. A meta-analysis of one randomised trial and six cohort studies with 1,011 men found late grade 2 or worse rectal effects of 1.5 against 5.7 per cent (risk ratio 0.23, 95 per cent confidence interval 0.06 to 0.99). With four-week hypofractionated treatment, a randomised trial of a hyaluronic acid spacer in 201 men found acute grade 2 or worse bowel effects in 2.9 against 13.8 per cent.

The harms the trials did not show. A review of the United States device-reporting database from 2015 to May 2023, against 206,619 devices sold, found 990 reported adverse events, including 91 abscesses and 91 fistulas, 123 of grade 3 or worse and five deaths; 35 events occurred before radiotherapy began, pointing at the device rather than the radiation. Reporting databases cannot give a rate, but they show complications more serious than the trials recorded.

The guidance. NICE HealthTech guidance 659 (formerly IPG752, 2023) states that the evidence on safety and efficacy "is limited in quality" and that the procedure "should only be used with special arrangements for clinical governance, consent, and audit or research". That is why this record is graded promising rather than proven: the dosimetric gain is reliable, the clinical benefit is modest in absolute terms and the rare harms are serious. Adoption is not measured by any source OnCo found for the NHS.

## Fields

- Kind: Idea
- Last checked: 2026-10-20
- Tags: protocol-upgrade; upgrade:promising; evidence:moderate
- Hypothesis: Offering a rectal spacer with written information on both its benefit and its rare serious complications, with every procedure entered in a national audit, reduces late grade 2 or worse bowel toxicity after prostate radiotherapy without a serious-complication rate above 1 per cent.
- Rationale: Randomised trials show a consistent reduction in rectal dose and bowel toxicity, and the reporting data show harms the trials were too small to see; the gap is a registry that measures both in the same men.
- Proposed test: A prospective national registry of every spacer placement with procedure complications, delivered rectal dose and patient-reported bowel function at two years, compared with contemporaneous men treated without a spacer by propensity matching.
- Maturity: early-clinical
- Actor: clinic

## Sources

- Mariados et al., Hydrogel spacer prospective multicenter randomized controlled pivotal trial (International Journal of Radiation Oncology, Biology, Physics 2015): https://doi.org/10.1016/j.ijrobp.2015.04.030
- Miller et al., Association of the placement of a perirectal hydrogel spacer with the clinical outcomes of men receiving radiotherapy for prostate cancer: a systematic review and meta-analysis (JAMA Network Open 2020): https://doi.org/10.1001/jamanetworkopen.2020.8221
- Mariados et al., Hyaluronic acid spacer for hypofractionated prostate radiation therapy: a randomized clinical trial (JAMA Oncology 2023): https://doi.org/10.1001/jamaoncol.2022.7592
- Millot et al., Major complications and adverse events related to use of SpaceOAR hydrogel for prostate cancer radiotherapy (Urology 2024): https://doi.org/10.1016/j.urology.2023.12.034
- NICE HealthTech guidance 659: biodegradable spacer insertion to reduce rectal toxicity during radiotherapy for prostate cancer: https://www.nice.org.uk/guidance/htg659

## Connected records

- 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/), [Four weeks or five treatments, not seven and a half weeks, for prostate radiotherapy](https://onco.cc/ideas/idea-pu-prostate-hypofractionation-default/)
- cancers: [Prostate cancer](https://onco.cc/cancers/prostate/)
- fronts: [Radiation Therapy](https://onco.cc/fronts/radiation/)
- technologies: [Bowel function after pelvic radiotherapy](https://onco.cc/technologies/bowel-after-pelvic-radiotherapy/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [SBRT / SABR (stereotactic radiotherapy)](https://onco.cc/technologies/sbrt/)
- institutions: [National Institute for Health and Care Excellence](https://onco.cc/institutions/nice/)
- bottlenecks: [Toxicity and quality of life are undervalued](https://onco.cc/bottlenecks/b-toxicity-qol/)

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