# Impact of Hydrogel Spacer Insertion on Radiation Dose to Erectile Structures and Longitudinal Sexual Function in Prostate Cancer Patients

## TL;DR

Hydrogel spacers reduce radiation to erectile structures in prostate cancer patients, but this does not prevent long-term sexual function decline.

## Contribution

This study is the first to show that hydrogel spacers reduce radiation dose to erectile structures but do not preserve sexual function over time.

## Key findings

- Hydrogel spacers significantly reduced radiation dose to neurovascular bundles and the right perineal artery.
- Despite dose reduction, sexual function declined over time, consistent with typical post-radiation changes.
- Spatial displacement of anatomy was confirmed, but no significant preservation of sexual function was observed.

## Abstract

Erectile dysfunction is a common long-term side effect for men receiving radiation therapy for prostate cancer. Hydrogel spacers are designed to protect nearby structures involved in sexual function by increasing the distance between the prostate and surrounding tissues. The aim of our retrospective study was to determine whether hydrogel spacer insertion reduces radiation exposure to erectile structures and whether this results in better long-term sexual function. In a cohort of 117 patients, we observed that hydrogel spacers lowered the radiation dose delivered to the neurovascular bundles and one of the perineal arteries and caused measurable displacement of surrounding anatomy. Despite these technical improvements, sexual function declined over time in a pattern consistent with typical post-radiation changes. These findings suggest that while hydrogel spacers effectively reduce radiation to key structures, this dose reduction alone may not be sufficient to preserve erectile function after treatment.

Background: Erectile dysfunction is a common late effect of prostate radiotherapy. Hydrogel spacers aim to reduce radiation exposure to nearby structures by increasing the distance between the prostate and surrounding tissues, potentially preserving sexual function. Methods: In this retrospective cohort study of 117 prostate cancer patients who received hydrogel spacers, we compared pre- and post-insertion radiation dose and anatomical positioning of erectile structures using paired t-tests. Longitudinal sexual function, assessed via EPIC scores, was modeled using linear mixed-effects regression with natural splines (df = 3), incorporating random intercepts and slopes to account for within-subject variability. Results: Spacer insertion significantly reduced radiation dose to the left and right neurovascular bundles (mean reductions: 1.66 Gy, 95% CI: 1.32–2.00; and 1.64 Gy, 95% CI: 1.28–2.01, respectively; p < 0.01) and the right perineal artery (1.33 Gy, 95% CI: 0.57–2.09; p < 0.01). No significant dose changes were observed for the penile bulb or left perineal artery, nor in anatomical distances. However, spatial displacement was confirmed by significant overlap and integrated volume changes. Longitudinal modeling showed a significant decline in sexual function between 12 and ≥36 months post-treatment (Spline 2: β = –12.72, 95% CI: −18.52–−6.92 and Spline 3: β = –6.68, 95% CI: −10.96–−2.40; p < 0.01). Conclusions: Hydrogel spacer insertion was associated with significant reductions in radiation dose to erectile structures, most notably the neurovascular bundles and the right perineal artery. However, longitudinal analyses revealed no corresponding preservation of sexual function. These findings suggest that while hydrogel spacers effectively reduce radiation exposure to key anatomical structures, their clinical benefit for maintaining erectile function remains uncertain.