Purpose

This study primarily aimed to evaluate the effects of a hydrogel spacer (HS) on dosimetric distribution in the planning target volume as well as on rectal and urethral doses in high-dose-rate brachytherapy (HDR-BT) for prostate cancer, and to identify prostate sub-regions with improved dosimetric parameters and patient conditions that particularly benefit from the use of HS.

Material and methods

This study included 28 patients, who underwent HDR-BT using HS. Treatment plans with HS and simulated plans without HS were compared. The prostate was divided into six regions: ventral and dorsal in the dorsoventral direction, and apex, mid-gland, and base in the craniocaudal direction. V100% and D90% were evaluated in each region, along with dose assessments for the rectum and urethra. Paired t-tests were performed to analyze significance, and effect sizes were calculated using Cohen’s d.

Results

S significantly improved V100% in the dorsal regions (p < 0.05), particularly in the dorsal apex and dorsal mid regions (median V100% with and without HS: apex, 100.00 vs. 97.10; mid, 100.00 vs. 97.22). D90% showed improvement across all regions (p < 0.05), with greater effects observed in the dorsal apex and dorsal mid regions (median D90% with and without HS: apex, 110.15 vs. 103.56; mid, 113.31 vs. 106.21; d ≥ 0.8). Rectal dose parameters improved significantly (p < 0.05), whereas urethral dose changes were not significant (p = 0.14).

Conclusions

HS effectively reduced rectal doses and improved V100% and D90% in the dorsal apex and dorsal mid regions of the prostate. These regions are anatomically closer to the rectum and are often subject to dose constraints as well as critical areas for sufficient dose delivery because of the frequent localization of prostate cancer lesions. Therefore, HS is particularly beneficial for patients with dominant lesions in these regions.