184 - A Randomized Comparison of Low Dose Rate or High Dose Rate Brachytherapy Combined with External Beam Radiation for Unfavorable Intermediate or High Risk Prostate Cancer: Efficacy Results at Median 6 Y

J. M. Crook¹, J. C. Cheng², N. Moideen³, G. Arbour³, F. Castro⁴, C. D. Araujo¹, D. Batchelar², R. M. Halperin⁵, D. J. W. Kim¹, D. W. Petrik¹, J. Rose⁶, and F. Bachand⁷; ¹BC Cancer, Kelowna, BC, Canada, ²University of British Columbia, Kelowna, BC, Canada, ³University of British Columbia, Vancouver, BC, Canada, ⁴Fundacion Peruana de Cancer, Lima, Peru, ⁵BCCancer, Kelowna, BC, Canada, ⁶BC Cancer Agency, Abbotsford, BC, Canada, ⁷CHU de Quebec - Hotel Dieu de Qc, Quebec, QC, Canada

Purpose/Objective(s): This single center randomized trial compared health-related QOL for men with unfavorable localized prostate cancer treated with combined pelvic external beam radiation (EBRT) and prostate brachytherapy (BT), randomly selected for either High Dose Rate (HDR) or Low Dose Rate (LDR). We now report the efficacy outcomes with a minimum 5 year follow up. Materials/

Methods: Consenting patients receiving pelvic EBRT (46Gy/23) combined with prostate BT were randomized to either LDR (110Gy) or HDR (15Gy) boost. HDRBT preceded EBRT by one week, while LDRBT followed. Androgen deprivation was used in 76%, beginning with 3 months neoadjuvant and continued for median 12 months. EBRT delivered 46 Gy/23 fractions using IMRT or VMAT in 68% and 3DcRT in 32%. Image guidance was either daily cone beam CT or implanted fiducials. All patients were followed up at 1-, 3-, and 6-mo, every 6 mo to 3 years, then annually. PSA = 0.2 at 4 years defined cure. Biochemical failure-free survival (bFFS), and overall survival (OS) were calculated by Kaplan Meier methods.
Results: From 01/2014 to 12/2019, a random number generator assigned 191 men (42% IR/ 58% HR): 108 to HDR and 87 to LDR. Median age was 71. Clinical stage was T1c in 15%, T2a/b in 48%, T2c/T3a in 35% and T3b in 2%. 43% had Gleason 8 or 9. Median PSA was 11.6 ng/ml, mean 27.0 ng/ml, max 145 ng/ml. The median follow up was 73 months (43m – 116m). The median PSA nadir was 0.07 in HDR and 0.08 in LDR (p=0.16). The median time to PSA nadir was 13.8 mo in HDR and 14.1 in LDR (p=0.87). At four years, 81% of HDR and 83% of LDR had a PSA = 0.2 (p=0.91). At five years, bFFS (nadir+2) for HDR and LDR were 94% and 90% respectively, and at 8 years 86% and 85% respectively. The 8-year OS for HDR and LDR was 73% and 70%. One patient in each arm had intraprostatic local failure. All failures were identified by imaging (CT, bone scan and/or PSMA PET) +/- biopsy if conventional staging negative and PET not available. 12 failures were distant, 3 regional and 2 combined regional and distant.
Conclusion: Previously reported primary QOL endpoint (ASTRO 2022) confirmed faster symptom recovery for HDR patients. In this small, randomized comparison, efficacy analysis shows no difference between LDR and HDR boost in biochemical disease-free survival at 5 and 8 years and confirms the excellent efficacy of dose escalation using a prostate brachytherapy boost as documented in the Ascende-RT trial for unfavorable localized prostate cancer.