Single-dose radiotherapy (SDRT) in the management of intermediate risk prostate cancer: Early results from a phase II randomized trial.
128 Background: To report initial response, acute treatment-related toxicity and patient-reported quality of life (QoL) after 24Gy SDRT derived from a randomized Phase II study of patients with intermediate-risk adenocarcinoma of the prostate (NCCN definition). Methods: Between November 2015 and December 2016, 30 hormone-naïve patients were enrolled in an IRB-approved prospectively randomized phase II study to receive either 45Gy in 5 consecutive daily fractions (Hypo-SBRT) or 24Gy SDRT. Treatment was based on VMAT-IGRT with urethral sparing via a dose-painting technique and real-time motion management with beacon transponders. The PTV included the MR-delineated prostate gland and seminal vesicles with 2 mm margin. Precise PTV targeting and anatomical reproducibility was achieved via placement of an endorectal air-filled balloon (150 cc) and a Foley catheter. This setup also conferred organ motion mitigation, and online tracking ensured treatment delivery within the 2 mm PTV margin.. Genito-urinary (GU) and gastro-intestinal (GI) toxicity were graded according to the NCI CTCAE v.4, and QoL was assessed by EPIC and IPSS questionnaires. Tumor response was assessed biochemically (PSA) and by follow-up MRI at 3 months after treatment and at 6 months intervals thereafter. Results: With a median follow-up of 16 months (range, 11-24), no grade ≥2 acute GI or GU toxicities were observed in either group. There were no significant differences in mean EPIC scores in all domains. An initial 6% and 8% drop in the EPIC urinary domain score occurred in the hypo and SDRT arm respectively, returning to baselines by 3 months. . PSA reduction kinetics were similar between the two regimens, reaching ≤1 ng/mL by 18 months. Of note, all cases, regardless of treatment regimen, converted to non-detectable disease on MRI at 6 months. Patients in this trial will receive a planned 24 months post-treatment biopsy to validate treatment outcome. Conclusions: These early trial outcomes indicate that 24Gy SDRT can be consistently and safely delivered, yielding the same low acute toxicity as demonstrated with the hypo 5x9Gy schedule, and is associated with excellent QoL measures. Clinical trial information: NCT02570919.