QP 22 - Phys 12: Dosimetry and Response Prediction
1125 - Assessing the Feasibility and Dosimetric Impact of a Non-Animal Stabilized Hyaluronic Acid (NASHA) Rectal Spacer in High-Dose-Rate Brachytherapy for Prostate Cancer
University of Virginia School of Medicine Charlottesville, VA
R. Patel1, A. D. Rao2, X. Zhu3, A. Copeland3, B. Kebede3, M. Alcock3, A. Loyd3, W. Nie3, M. Joo3, J. Fan3, and D. W. Kim3; 1University of Virginia School of Medicine, Charlottesville, VA, 2Inova Schar Cancer Institute, Falls Church, VA, 3Inova Schar Cancer Institute, Fairfax, VA
Purpose/Objective(s): Injectable spacers placed between the prostate and rectum before radiation therapy (RT) for prostate cancer can reduce the dose to the adjacent rectum. While this method has been studied extensively with external beam RT, there is limited data for its use in high-dose-rate brachytherapy (HDR-BT). Additionally, a new formulation using non-animal stabilized hyaluronic acid (NASHA) allows for improved anatomic visibility and thus may better facilitate accurate spacer placement, minimizing complications. This study aims to assess the feasibility and dosimetry of NASHA rectal spacer utilization during HDR-BT. Materials/
Methods: This single-center study retrospectively reviewed consecutive patients with prostate cancer who received HDR-BT from 2021-2024. A subset received a NASHA rectal spacer via a transperineal approach under transrectal ultrasound guidance and returned 2-4 weeks after placement to undergo HDR-BT. Dosimetric variables were compared between patients with and without spacers using two sample t-tests. Results: 76 patients received HDR-BT, 13 with a spacer and 63 without a spacer, including two patients for whom spacer implantation was intended but unachievable due to a small rectal-prostate interface. Median age was 67 years. Prostate cancer stage included low risk (n=1), favorable intermediate risk (n=23), unfavorable intermediate risk (n=22), high risk (n=21), very high risk (n=8), and node-positive (n=1). Median baseline PSA was 7.05 ng/mL (range 1.93 – 292). A total of 107 HDR-BT treatments were administered (21 spacer, 86 non-spacer). 23 patients (6 spacer, 17 non-spacer) were treated with prostate monotherapy (27 Gy in 2 fractions), 2 patients (1 spacer, 1 non-spacer), with salvage brachytherapy, and 51 patients (6 spacer, 45 non-spacer) with HDR brachytherapy boost and external beam RT. Mean prostate volume was 48.1cc. Use of a rectal spacer resulted in a reduction in mean rectal D0.1cc and V75% (80.0% vs 84.7%, p<0.0001; 0.69cc vs 0.93cc, p=0.0170, respectively). Patients treated with a rectal spacer had a higher mean prostate V125% (60.9% vs. 58.7%, p=0.0167). There were no differences in prostate V100% and V200%, urethra D0.1cc, and bladder D0.1cc between groups (p>0.05). Rectal spacer did not negatively impact the feasibility of HDR-BT catheter placement under ultrasound guidance, nor were there complications from placement. Conclusion: A NASHA rectal spacer can be placed prior to prostate HDR-BT to successfully increase the distance between the rectum and prostate without interfering with visibility and technical delivery of HDR-BT. Use of a rectal spacer effectively reduces dose to the rectum, while maintaining appropriate target coverage to the prostate. Future investigations will be performed to assess the impact of rectal spacer use on acute and late gastrointestinal toxicity.