Combined Hypofractionated Radiation Therapy and Brachytherapy for Managing Prostate-Specific Membrane Antigen Positron Emission Tomography-Staged Organ-Confined Prostate Cancer: Primary Endpoint Analysis of a Prospective Study.

Purpose: This study aims to evaluate the primary endpoint of a phase 2 prospective trial, which included a patient cohort staged with 18F-prostate-specific membrane antigen positron emission tomography/computed tomography (CT), treated with a combination of prostate high dose-rate brachytherapy and prostate/seminal vesicles external beam radiation therapy for intermediate and high-risk prostate cancer.

Methods and materials: Forty-one patients with unfavorable intermediate, high risk (HR), and very HR prostate cancer were recruited to receive a combination of hypofractionated external beam radiation therapy to the prostate ± seminal vesicles of 36 Gy (12 fractions of 3 Gy each) delivered in consecutive days, followed by single-fraction real-time high-dose-rate brachytherapy of 14 Gy. Patients also received risk-adjusted androgen deprivation therapy (ADT). All patients were primarily conventionally staged with prostate multiparametric magnetic resonance imaging, abdomen/pelvis CT, and bone scintigraphy, receiving an additional prostate-specific membrane antigen positron emission tomography/CT before their study inclusion. Urinary, gastrointestinal symptomatology, sexual potency and acute, as well as early late toxicity, were assessed using various questionnaires (International Prostate Symptom Score, International Index for Erectile Function, Extended Prostate cancer Index Composite for Clinical Practice, Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer).

Results: Forty-one patients (based on National Comprehensive Cancer Network stratification system 48.8% unfavorable intermediate, 43.9% HR, and 7.3% very HR) completed treatment and reached at least 12 months of follow-up at the time of the current analysis. Median follow-up was 20 months (IQR, 13-28). Median age was 71.7 years, median prostate specific antigen before treatment was 8.4 ng/mL (5.0-28.3), and median volume of the prostate was 36.6 cc (14.9-68.2). Short-term ADT was administered to 43.9% of patients, whereas 48.8% received long-term ADT; the rest of the patients did not receive hormonal therapy. No severe (grade ≥3) acute events were recorded. An increase was observed in the prevalence of grade 2 genitourinary toxicity, owed mainly to nocturia (2.4% at 3 months, 4.9% at 6 months, and 26.8% at 12 months), with grade 1 remaining stable over this period. Regarding gastrointestinal toxicity, grade 1 and 2 incidences remained low and almost unchanged over this time interval. A significant decline from baseline compared to 3 months post treatment was observed both in hormonal and sexual domains, with high severity exhibited as a worsening from 12% to 38% and from 0% to 5%, respectively. No other domains exhibited any significant decline (urinary incontinence, irritation/bother, and bowel).

Conclusions: The evaluation of the primary results of the presented prospective phase 2 trial suggests that this hypofractionated combined radiotherapeutic scheme is well tolerated, presenting no early severe adverse events. Moreover, patient-reported outcomes confirm these results because no significant decline in any domain from baseline values was recorded.