Rectal spacers are widely used to reduce rectal dose in prostate radiotherapy. However, their use during transrectal ultrasound (TRUS)-guided high-dose-rate (HDR) brachytherapy has been limited by degradation of ultrasound image quality when placed on the day of the procedure, often necessitating CT-based planning or separate-day workflows.
To evaluate the feasibility and dosimetric impact of same-day hyaluronic acid (HA) rectal spacer injection in patients undergoing TRUS-guided HDR prostate brachytherapy.
Following institutional review board approval, a retrospective analysis was performed on 20 patients with clinically localized prostate cancer treated with HDR brachytherapy combined with external beam radiation therapy between April 2023 and March 2024. Ten patients with a prostate-anterior rectal wall distance < 5 mm received HA rectal spacer injection immediately prior to HDR brachytherapy, while ten patients with a distance > 5 mm did not undergo spacer placement. HA spacer (3-6 cc) was injected into the perirectal space under sagittal TRUS guidance, followed by catheter placement and real-time TRUS-based treatment planning. A single fraction of 15 Gy was delivered. Dosimetric parameters were compared using an unpaired two-tailed Student's t-test.
HA rectal spacer placement was technically successful in all patients (10/10) and preserved ultrasound image quality for catheter placement and treatment planning. Spacer placement improved prostate V100 (95.6% ± 0.5% vs. 94.5% ± 0.6%; p < 0.001) and significantly reduced rectal V75 (0.42 ± 0.25 cc vs. 0.97 ± 0.34 cc; p < 0.001). No significant differences were observed in urethral D10 or bladder D0.1cc.
Same-day HA rectal spacer injection is feasible during TRUS-guided HDR prostate brachytherapy and preserves ultrasound image quality, enabling fully real-time treatment planning without the need for CT-based workflows. This approach provides rectal dose reduction while maintaining target coverage and may offer a streamlined alternative to multistep spacer placement strategies.
Journal of applied clinical medical physics. 2026 Jul [Epub]
Sook Kien Ng, Damodar Pokhrel, Colin Huang, Francis Adumata Asamoah, Jordan Alexander Holmes, Arpan Prabhu, Omar Ishaq
Department of Radiation Oncology, Indiana University School of Medicine, Indianapolis, Indiana, USA.