3210 - High Dose-per-Fraction Definitive Radiotherapy after Prior Ablative Treatment of Prostate Cancer
Presenter(s)
P. T. Courtney1, J. E. Juarez Casillas1, S. Ebrahimi1, E. Y. Lin1, M. A. Eala2, A. Lee1, P. S. Venkat1, L. Valle1, A. J. Chang1, A. U. Kishan1, and M. L. Steinberg1; 1Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA, 2University of the Philippines, Manila, Philippines
Purpose/Objective(s): Ablative treatment of localized prostate cancer has increased in recent years. Data on radiotherapy in the local salvage setting are limited, particularly for high dose-per-fraction techniques such as stereotactic body radiotherapy (SBRT) and high dose rate brachytherapy (HDR-BT).
Materials/Methods: This is a single-site, retrospective cohort study of patients with locally recurrent prostate cancer treated with SBRT (CT- or MRI-guided) or HDR-BT between 2018-2024 after prior ablative therapy failure. We measured the rates of genitourinary (GU) and gastrointestinal (GI) CTCAE toxicity and disease recurrence after salvage radiotherapy.
Results: We identified 49 patients (median age 72 years) with a median follow-up of 25 months (IQR 11-42) from salvage radiotherapy. 21 (43%) received ultrasound-based ablation, 20 (41%) received cryotherapy, 7 (14%) received laser ablation, and 1 (2%) received irreversible electroporation. 34 (69%) ablations were whole gland, and 10 (20%) patients received more than one ablation, including 5 (10%) who had received prostate radiotherapy in addition to ablation, prior to salvage radiotherapy. At radiotherapy, 4 (8%) had favorable intermediate, 11 (22%) had unfavorable intermediate, 19 (39%) had high, and 2 (4%) had very high risk disease per NCCN guidelines. Additionally, 6 (12%) had nodal and 7 (14%) had oligometastatic disease. The median time from initial ablation to radiotherapy was 40 months (IQR 24-73). For radiotherapy technique, 26 (53%) received MRI-guided SBRT, 11 (22%) received CT-guided SBRT, and 12 (25%) received HDR-BT. The median dose and fractions for SBRT were 40 Gy (range 34-40 Gy) and 5 (all), respectively, and for HDR-BT were 27 Gy (range 15-36 Gy) and 2 (range 1-6), respectively. 43 (88%) radiotherapy plans were whole gland. The median GU and GI toxicity grades immediately prior to salvage radiotherapy were 1 and 0, respectively. 14 (29%) and 8 (16%) patients total developed new grade =2 GU and GI toxicity after radiotherapy, respectively. Across modalities, the rates of new grade =2 GU toxicity were 27%, 45%, and 17% for MRgSBRT, CTgSBRT, and HDR-BT, respectively; these differences were not significant by Fisher’s exact test. The rates of new grade =2 GI toxicity were 19%, 27%, and 0% for MRgSBRT, CTgSBRT, and HDR-BT, respectively; these differences were not significant by Fisher’s exact test. There were 1 (2%) and 1 (2%) new grade 3 GU and GI toxicities after CTgSBRT and MRgSBRT, respectively. 5 (10%) patients experienced disease recurrence after radiotherapy. There were 3 (6%) local recurrences, of which 2 were local only and 1 was local and distant. Of these 3 patients with local recurrence, 1 had received whole gland HDR-BT, and 2 had received MRI-guided SBRT (1 whole and 1 partial gland).
Conclusion: In one of the largest series on salvage high dose-per-fraction radiotherapy after prostate ablation, we found overall low rates of high grade toxicity and disease recurrence albeit with some variability among radiotherapy modalities.