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

Abstract

Importance: 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.

Objective: To evaluate the association between perirectal hydrogel spacer placement and clinical outcomes of men receiving radiotherapy for prostate cancer.

Data sources: A systematic search was performed of the Cochrane Central Register of Controlled Trials, MEDLINE, and Embase for articles published through September 2019.

Study selection: Studies comparing men who received a hydrogel spacer vs men who did not receive a spacer (controls) prior to prostate radiotherapy.

Data extraction and synthesis: Via random-effects meta-analysis, group comparisons were reported using the weighted mean difference for continuous measures and the risk ratio for binary measures.

Main outcomes and 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).

Results: 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]).

Conclusions and relevance: 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.

Figure 1.. Rectal Irradiation With vs Without Perirectal Hydrogel Spacer

The mean difference and 95% CI between hydrogel spacer and control groups in the percentage of rectal volume receiving at least 70 Gy irradiation are plotted for each study (with inverse-variance weighting method and random-effect model). The size of the square is proportional to the sample size of the study. The pooled mean difference denoted by the diamond apex, and the 95% CI is denoted by the diamond width. A pooled mean difference of less than 0 indicates less rectal irradiation with hydrogel spacer; a value greater than 0 indicates more rectal irradiation with hydrogel spacer. The pooled percentage of rectal volume receiving at least 70 Gy irradiation was 3.5% with hydrogel spacer and 10.4% with controls (mean difference, −6.5%; P < .001). Significant heterogeneity among studies was identified (I² = 97%; P < .001).

Figure 2.. Late Grade 2 or Higher Rectal Toxic Effects With vs Without Perirectal Hydrogel Spacer

The risk ratio (RR) and 95% CI between hydrogel spacer and control groups are plotted for each study (with inverse-variance weighting method and random-effect model). The size of the square is proportional to the sample size of the study. The pooled RR is denoted by the diamond apex, and the 95% CI is denoted by the diamond width. A pooled RR of greater than 1 indicates higher risk with controls. A pooled RR of less than 1 indicates lower risk with hydrogel spacer. Late grade 2 or higher rectal toxic effects were significantly lower in the hydrogel spacer group (1.5% vs 5.7%; RR, 0.23; P = .05). Significant heterogeneity among studies was not identified (I² = 24%; P = .27).

Figure 3.. Change in Late Bowel-Related Quality of Life (QoL) With vs Without Perirectal Hydrogel Spacer

The mean difference and 95% CI between hydrogel spacer and control groups are plotted for each study (with inverse-variance weighting method and random-effect model). The size of the square is proportional to the sample size of the study. The pooled mean difference denoted by the diamond apex, and the 95% CI is denoted by the diamond width. A pooled mean difference of less than 0 indicates lower bowel-related QoL with hydrogel spacer; a value greater than 0 indicates higher bowel-related QoL with hydrogel spacer. Bowel-related QoL reported on a 0 to 100 scale, where higher values indicate better QoL. Late bowel-related QoL was significantly higher in the hydrogel spacer group (mean difference, 5.4; P < .001). Significant heterogeneity among studies was not identified (I² = 0%; P = .76).