Association of the Placement of a Perirectal Hydrogel Spacer With the Clinical Outcomes of Men Receiving Radiotherapy for Prostate Cancer

Abstract

Perirectal spacers are intended to lower the risk of rectal toxic effects associated with prostate radiotherapy. A quantitative synthesis of typical clinical results with specific perirectal spacers is limited. To evaluate the association between perirectal hydrogel spacer placement and clinical outcomes of men receiving radiotherapy for prostate cancer. A systematic search was performed of the Cochrane Central Register of Controlled Trials, MEDLINE, and Embase for articles published through September 2019. Studies comparing men who received a hydrogel spacer vs men who did not receive a spacer (controls) prior to prostate radiotherapy. Via random-effects meta-analysis, group comparisons were reported using the weighted mean difference for continuous measures and the risk ratio for binary measures. Procedural results, the percentage volume of rectum receiving at least 70 Gy radiation (v70), early (≤3 months) and late (>3 months) rectal toxic effects, and early and late changes in bowel-related quality of life on the Expanded Prostate Cancer Index Composite (minimal clinically important difference, 4 points). The review included 7 studies (1 randomized clinical trial and 6 cohort studies) involving 1011 men (486 who received a hydrogel spacer and 525 controls), with a median duration of patient follow-up of 26 months (range, 3-63 months). The success rate of hydrogel spacer placement was 97.0% (95% CI, 94.4%-98.8% [5 studies]), and the weighted mean perirectal separation distance was 11.2 mm (95% CI, 10.1-12.3 mm [5 studies]). Procedural complications were mild and transient, occurring in 0% to 10% of patients within the studies. The hydrogel spacer group received 66% less v70 rectal irradiation compared with controls (3.5% vs 10.4%; mean difference, -6.5%; 95% CI, -10.5% to -2.5%; P = .001 [6 studies]). The risk of grade 2 or higher rectal toxic effects was comparable between groups in early follow-up (4.5% in hydrogel spacer group vs 4.1% in control group; risk ratio, 0.82; 95% CI, 0.52-1.28; P = .38 [6 studies]) but was 77% lower in the hydrogel spacer group in late follow-up (1.5% vs 5.7%; risk ratio, 0.23; 95% CI, 0.06-0.99; P = .05 [4 studies]). Changes in bowel-related quality of life were comparable between groups in early follow-up (mean difference, 0.2; 95% CI, -3.1 to 3.4; P = .92 [2 studies]) but were greater in the hydrogel spacer group in late follow-up (mean difference, 5.4; 95% CI, 2.8-8.0; P < .001 [2 studies]). For men receiving prostate radiotherapy, injection of a hydrogel spacer was safe, provided prostate-rectum separation sufficient to reduce v70 rectal irradiation, and was associated with fewer rectal toxic effects and higher bowel-related quality of life in late follow-up.