A Pilot Study of Ultra-High-Dose Hypofractionated or Single-Dose Radiotherapy for Intermediate Risk Prostate Cancer

The present study evaluates clinical outcomes and treatment-related toxicity following definitive ultra-high dose external beam radiotherapy delivered with two different regimens in patients with intermediate-risk adenocarcinoma of the prostate. Modern computer-driven technology enables the implementation of ultra-high hypofractionated Image-Guided Radiotherapy (IGRT) safely. Prostate cancer patients classified according to the current National Comprehensive Cancer Network (NCCN) guidelines as intermediate risk (biopsy Gleason score of 7 and/or Prostate Specific Antigen (PSA) level \>10 and ≤20 ng/mL and/or Stage T1, T2a, T2b or T2c) are eligible for this study. Patients will undergo IGRT with volumetric intensity-modulated arc radiotherapy (VMAT) with state-of-the-art treatment-planning and quality assurance procedures. Emphasis is placed on normal tissue sparing and delivery accuracy via the use of devices that ensure stability and beam location reproducibility. A rectal balloon with air filling will be used for prostate target immobilization and anatomical reproducibility, while a urethral catheter loaded with beacon transponders will be used to ensure set-up reproducibility and online target tracking. Previously untreated patients with intermediate-risk prostate cancer will be prospectively randomized to receive either 45 Gy in five fractions of 9 Gy each vs. 24 Gy in a single-dose. Patients will be followed at one month post-treatment and every 3 months for up to 12 months (+/- 4 weeks) and every 6 months thereafter. Acute and chronic toxicity evaluations will focus on urinary, rectal and sexual functions and will be assessed through validated questionnaires. Serum PSA values will be regularly acquired during follow-up. A multiparametric MRI will be performed at baseline, 6, 12 and 24 months following intervention. Additionally, a post-treatment diffusion-weighted MRI (DW-MRI) will be performed within 15 minutes of the first treatment, to measure early physiologic changes, such as perfusion and ischemia, that may correlate with clinically relevant end-points. Post-treatment prostate needle biopsies will be obtained at 24 months to evaluate pathologic response to therapy. The study will be continuously monitored for a minimum of 5 years. In the event unexpected severe (grade ≥3) toxicities are observed in any one of the treatment arms, the study will be terminated according to the stopping rule \>3/first 15 patients.