Princess Margaret Cancer Center, University Health Network Toronto, ON
C. Johnny, A. Berlin, A. McPartlin, C. Catton, R. Glicksman, S. Raman, P. Chopade, R. A. Weersink, J. Winter, J. Dang, and P. Chung; Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada
Purpose/Objective(s): Report the outcomes of a prospective study of focal MR-guided HDR (MRgHDR) brachytherapy boost in combination with stereotactic body radiotherapy (SBRT) for localized prostate cancer.Materials/
Methods: Eligible patients included intermediate-risk (IR) and high-risk (HR) prostate cancer patients with visible gross disease (at 1 or more intraprostatic sites) comprising less than 33% of the total prostate volume on diagnostic MRI. Patients underwent either a 15 Gy single fraction MRgHDR focal boost to the gross disease followed by SBRT, 30 Gy/5 fractions for IR disease (prostate only) or 30 Gy/5 fractions for HR disease (prostate + pelvic nodes). Outcomes included PSA, toxicity (CTCAE v4), Health-Related Quality of Life (HRQoL) assessments (Expanded Prostate Cancer Index Composite) and were conducted at baseline, then at 1, 3, and 6 months, followed by 1, 2, 3, and 5 years. Androgen deprivation therapy (ADT) was administered based on risk category. At a minimum of two years post-radiation, patients underwent a prostate MRI with or without a systematic biopsy to assess local disease status. Biochemical failure was defined according to the Phoenix definition (nadir + 2). Results: Between 2017 and 2023, 153 patients were enrolled, with 128 (84%) having IR and 25 (16%) having HR disease. The median age was 69 years old (range 49-81), and the median PSA was 8ng/ml (2-53). ADT was administered in 46 (30%) patients. Among the IR patients who received ADT (25 patients), 21 (84%) patients received = 6 months of ADT, while 4 (16%) patients received > 6 months of ADT. Of the 21 patients from the HR group, 3 (14%) patients received 6 months of ADT, and 18 (86%) received > 6 months of ADT. Hydrogel spacer insertion was used in 72 (47%) patients. Median follow-up was 36 months (range, 2-79). Median PSA nadir in patients without ADT was 0.35 (Range 0.01-4.75). Overall, the 3-year biochemical control rate was 96.5%, with 96% and 100% in the IR and HR groups. No isolated local failure was observed at 3 years. 3 patients experienced local failure in conjunction with nodal relapse, and one patient had associated regional and distant failure. No isolated regional or distant failures occurred. 1 month after treatment, the incidence of acute grade > 2 genitourinary (GU) and gastrointestinal (GI) toxicities were 13% and 2.6%, respectively. By 6-months, these rates decreased to 2.6% and 1.4% for GU and GI toxicity, respectively. Late grade = 2 GU and GI toxicities at 1 year remained consistent at 2.6% and 0.7%. Notably, only one patient encountered severe toxicity (Grade 3 GU - hematuria attributed to radiation cystitis at 6 months), which subsequently resolved. Patients with a rectal spacer experienced slightly lower GI toxicity, and not statistically significant. No difference in GI toxicity was seen in patients who received pelvic nodal irradiation when compared to prostate-only patients. Conclusion: Focal MRgHDR brachytherapy combined with SBRT demonstrated favorable tolerability and promising local and biochemical control.
