K. K. D. Yeung1,2, C. D. Araujo1,2, D. Batchelar1,2, D. J. W. Kim1,2, D. W. Petrik1,2, T. Rose1, F. Bachand2, and J. M. Crook1,2; 1BC Cancer, Kelowna, BC, Canada, 2University of British Columbia, Kelowna, BC, Canada
Purpose/Objective(s): Brachytherapy (BT) boost is recommended for optimal dose escalation in radiation management of unfavorable organ-confined prostate cancer. High dose rate (HDR) BT is associated with faster symptom recovery than low dose rate BT. We report the clinical efficacy and toxicity of HDR prostate BT combined with external beam radiotherapy (EBRT) and evaluate the ability to achieve a 4-year PSA =0.2 ng/mL to predict freedom from prostate cancer recurrence long-term.Materials/
Methods: All patients treated with HDR BT from program initiation 06/2011 until 08/2019 at one institution were identified. Baseline patient and prostate cancer characteristics, treatment details, and clinical endpoints including clinical failure, toxicity, and PSA response were collected. Results: 325 patients with localized prostate cancer treated with HDR prostate BT combined with EBRT were identified. Disease stratification was 179 high risk, 145 high tier intermediate, and 1 low tier intermediate. Grade group (GG) distribution was 21% GG 2, 39% GG 3, 11% GG 4, and 29% GG 5. Clinical T stage was 34% T1c/T2a, 48% T2b/T2c, 17% T3a/b, 0.3% T4, and 1.2% Tx. Baseline PSA was <10 ng/mL in 41%, 10 to 20 ng/mL in 39%, and >20 ng/mL in 20 % of patients. Androgen deprivation was used in 72% with duration <6 mo in 7%, 6 to12 mo in 18%, 12 mo in 64%, and > 12 mo in 10%. HDR BT was 20 Gy/2 fractions for first 50 patients, a single 13.5 Gy for 1 patient, and 15 Gy/1 for the remaining patients. EBRT was delivered as 46 Gy/23 fractions in 98% of cases; using 3D conformal RT in 38%, intensity modulated RT in 5%, and volumetric modulated arc therapy in 57% of cases. EBRT targets were 68% whole pelvis, 20% mini pelvis, and 12% prostate and seminal vesicles. Median follow up is 77 months (range: 25-139). 17% of patients had biochemical failure. 11% were identified as distant and 3% as regional lymph node failure by conventional imaging or PSMA PET. 4% had local failure diagnosed by PSMA PET or biopsy. 82% of patients had no evidence of disease at last follow up. 4-year PSA is available for 274 patients, 79% of whom have a PSA =0.2 ng/mL. For these patients, at most recent follow up (median 76 mo, range: 46-139 mo), the median current PSA was 0.04 ng/mL and 97% were free of prostate cancer recurrence. CTCAE V5 late grade 2 urethral strictures were seen in 5% and grade 3 in 3%. CTCAE V5 late grade 2 genitourinary and gastrointestinal bleeding was 0.6% and 3.4%, respectively, with no grade 3 toxicity. Conclusion: HDR brachytherapy added to EBRT is an effective form of dose escalation for unfavorable localized prostate cancer. The very low rates of regional lymph node and prostate failure and minimal grade 3 toxicity have accelerated its rise to standard of care in our center.
