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).