Two-fraction prostate SABR vs. two-fraction HDR brachytherapy: does dose heterogeneity matter?
PO-1408
Abstract
Two-fraction prostate SABR vs. two-fraction HDR brachytherapy: does dose heterogeneity matter?
Authors: Rohann Correa1, Gerard Morton1, Hans Chung1, Chia-Lin Tseng1, Patrick Cheung1, William Chu1, Stanley Liu1, Merrylee McGuffin1, Anam Shahid1, Melanie Davidson1, Ananth Ravi2, Joelle Helou3, Yasir Alayed4, Liying Zhang1, Alexandre Mamedov1, Andrew Loblaw1
1Odette Cancer Centre, Sunnybrook Health Sciences Centre, Radiation Oncology, Toronto, Canada; 2Molli Surgical, Medical Devices, Toronto, Canada; 3Princess Margaret Cancer Centre, Radiation Oncology, Toronto, Canada; 4King Saud University, Radiation Oncology, College of Medicine, Riyadh, Saudi Arabia
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Purpose or Objective
Contemporary
radiotherapy for localized prostate cancer (PCa) is deliverable via stereotactic
ablative radiotherapy (SABR) and high dose rate (HDR) brachytherapy. Here we report on a parallel
cohort analysis of two prospective, phase II clinical trials of two-fraction prostate
SABR versus two-fraction HDR monotherapy.
Material and Methods
Enrolled patients had histologically-confirmed PCa (clinical stage T1c-T2b; grade group 1, 2, or 3; and PSA <20 ng/mL). SABR and HDR doses were 26 Gy and 27 Gy in 2 weekly fractions, respectively. Patient-level data from each cohort was analysed to assess prostate specific antigen (PSA) response kinetics, biochemical failure, toxicity, and quality of life (QOL).
Results
Thirty
patients receiving SABR and 83 receiving HDR were included. Fifty percent and 30% of patients had
unfavourable-intermediate risk disease, respectively. SABR patients had higher
mean baseline PSA (8.7 versus 6.8 ng/mL, p=0.016). Median follow-up was 72.7 and 65.3
months, respectively. Mean dose delivered to the prostate (Dmean) ranged from 26.6 to 26.8 Gy for SABR versus 35.5 to 45.5 Gy for HDR. Both cohorts achieved a median nadir PSA of 0.16 ng/mL at
a median of 57 months post-treatment. Nine patients in total experienced biochemical
failure, 1 following SABR (3.3%) and 8 following HDR (9.6%). Cumulative
BF probability (±SE)
at 72 months was 3.5% (±3.5%) for SABR versus 12.8% (±4.8%) and was not significantly different between cohorts (p=0.19). Low rates of CTCAE grade≥2 toxicity were observed in both cohorts. No
differences in EPIC scores over time were observed between cohorts.
Conclusion
Two fractions of SABR yields similar rates of biochemical failure, acute and late toxicities, and QOL as two factions of HDR brachytherapy. These hypothesis-generating data support the design of a randomized controlled trial to test a two-fraction SABR versus two-fraction HDR monotherapy.