Perirectal hydrogel spacer placement prior to radiation therapy (RT) for prostate cancer may be a prudent preventive strategy to reduce radiation-induced rectal toxic effects, investigators concluded based on a systematic review and meta-analysis.

Larry E. Miller, PhD, from Miller Scientific of Johnson City, Tennessee, and colleagues reviewed 7 studies involving 1011 men undergoing RT, of whom 486 received a hydrogel spacer (SpaceOAR, Boston Scientific) and 525 served as controls. The spacer is injected between the Denonvilliers fascia and anterior rectal wall prior to treatment. It provides perirectal separation through a typical 3-month course of RT and is completely metabolized after 6 months, according to the investigators.

The studies included 1 randomized clinical trial and 6 cohort studies. The median duration of follow-up was 26 months. The main outcomes and measures included procedural results, the percentage volume of rectum receiving at least 70 Gy radiation (v70), early (3 months or less) and late (more than 3 months) rectal toxic effects, and early and late changes in bowel-related quality of life on the Expanded Prostate Cancer Index Composite.

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Hydrogel placement was successful in 97% of cases, Dr Miller’s team reported in JAMA Network Open. The weighted mean perirectal separation distance was 11.2 mm.

The hydrogel spacer group received 66% less v70 rectal irradiation compared with controls. The risk of grade 2 or higher rectal toxic effects was comparable between the hydrogel spacer group and control arm in early follow-up, but was 77% lower in the spacer group in late follow-up.

In addition, changes in bowel-related QoL were comparable between the study arms at a 3-month follow-up, but were significantly better in the spacer arm in late follow-up (median 48 months).

“Overall, these results suggest that injection of an absorbable perirectal hydrogel spacer prior to RT for prostate cancer may reduce rectal irradiation and the associated rectal toxic effects that manifest clinically after longer-term follow-up,” Dr Miller and his colleagues concluded.


Boston Scientific funded the study and several authors reported being paid consultants for the company.


Miller LE, Efstathiou JA, Bhattacharyya SK, 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 [published online June 17, 2020]. JAMA Netw Open. 2020;3:e208221.