Hydrogel Spacer Insertion Prior to Stereotactic Body Radiation Therapy to the Prostate: A Comparative Study

The insertion of a hydrogel spacer between the rectum and prostate before stereotactic body radiation therapy (SBRT) for prostate cancer significantly reduces the radiation dose to the rectum. Despite the widespread use of this technique, clinical data remain sparse. The objective of this study was to investigate the clinical benefit of a hydrogel spacer in SBRT.

The database of a tertiary medical center was retrospectively searched for all patients with prostate cancer who underwent SBRT, with or without the insertion of a hydrogel spacer, between June 2013 and December 2018. The groups were compared for rectal and urinary toxicity (National Cancer Institute Common Terminology Criteria for Adverse Events v4) using the χ² test and t test. In addition, a subgroup analysis limited to patients receiving 37.5 or 40 Gy in 5 fractions was performed to account for the possible confounding effect of dose variability between the groups. Complications related to the procedure were also evaluated.

The cohort included 308 patients who underwent SBRT with (n = 227) or without (n = 75) the insertion of a hydrogel spacer. Rates of grade 2 or higher rectal toxicity were 31 of 223 patients (13.9%) in the spacer group and 9 of 75 patients (12%) in the nonspacer group. Corresponding rates of urinary grade 2 toxicity were 58 of 223 patients (26%) and 14 of 75 patients (18.6%), respectively. Neither difference was statistically significant. Similar findings were observed in the subgroup analysis. Severe complications related to the procedure occurred in 5 of 227 cases (2.2%).

This study did not demonstrate a significant effect of hydrogel spacer insertion on reducing rectal or urinary toxicity in patients with prostate cancer undergoing SBRT. Given the dual consideration of questionable clinical benefit and the risk of debilitating complications, additional studies should be performed on the selective use of this procedure.