Objectives: Rectal hydrogel spacers have become a key component of prostate radiotherapy planning, particularly with the growing use of hypofractionated and stereotactic body radiotherapy (SBRT). While the dosimetric and rectal toxicity benefits of spacing are well established, its effect on sexual function remains less well defined. This study evaluates longitudinal erectile function in patients treated with robotic SBRT with or without rectal spacing.

Methods: From 2020 to 2024, 209 patients with localized prostate cancer were treated with CyberKnife SBRT to a total dose of 36.25 Gy in 5 fractions. None received androgen deprivation therapy. Rectal spacers were placed by experienced urologists prior to simulation. Expanded Prostate Cancer Index Composite (EPIC) sexual function domain scores were collected at baseline, 4 months, and 12 months post-treatment. Changes from baseline, and rates of maintaining erections firm enough for intercourse were compared between spaced and non-spaced cohorts using two sample t-test at each time point.

Results: All patients had ≥12 months of follow-up with median age 70 years and mean prostate volume of 44 cc. The spaced cohort (n=209) and non-spaced cohort (n=24) were comparable at baseline, with similar pretreatment EPIC erectile function score (3.17 vs 2.83; p = 0.139). Patients receiving a rectal spacer demonstrated smaller declines in EPIC erectile function at 4 months (3.02 vs 2.11; p = 0.0005) and 12 months (2.92 vs 2.26; p = 0.0082). The proportion of men maintaining erections sufficient for intercourse at 12 months was higher in the spacer group (65% vs 38%), although this was not statistically significant (p = 0.149).

Conclusion(s): Rectal spacer placement was associated with improved preservation of sexual function following SBRT, with smaller declines in sexual QOL across the first post-treatment year. Although some differences did not reach statistical significance, the overall trend suggests a potential protective effect of rectal spacing on sexual health in men undergoing prostate SBRT.