Prospective Evaluation of Stereotactic Body Radiotherapy Boost for Unfavorable Localized Prostate Cancer

This study is designed to evaluate whether delivering a stereotactic body radiotherapy (SBRT) boost-a short course of five high-dose, precisely targeted radiation treatments-can safely and effectively replace the traditional invasive high dose rate (HDR) brachytherapy boost for men with unfavorable, high-risk, or very high-risk localized prostate cancer. The SBRT boost uses imaging-guided systems and gold fiducial markers to track prostate motion in real time, allowing submillimeter accuracy without placing needles inside the prostate. Treatment planning incorporates CT/MRI fusion, careful mapping of the urethra, and strict dose-volume limits for nearby organs such as the rectum and bladder to ensure the boost achieves HDR-equivalent tumor dosing while minimizing toxicity. All patients also receive standard external beam radiation therapy to the pelvis, and the combined course is designed based on biological dose modeling and prior HDR clinical experience to optimize tumor control while maintaining acceptable side-effect rates.

The protocol also includes structured follow-up and ongoing safety monitoring to track side effects, prostate-specific antigen (PSA) response, and quality-of-life outcomes. Patients are assessed at regular intervals-from two weeks post-treatment through five years-with physical exams, PSA testing, toxicity evaluations, and validated questionnaires measuring urinary and sexual function. Imaging such as prostate-specific membrane antigen (PSMA) PET/CT or bone scans is performed if biochemical failure or symptoms suggest disease progression. The study's primary goals are to determine the rate of significant gastrointestinal and genitourinary side effects and to measure biochemical disease-free survival at five years, while secondary goals include evaluating local and distant tumor control and longer-term survival outcomes. Stopping rules, adverse-event reporting procedures, and quality-assurance requirements are built into the protocol to ensure patient safety and regulatory compliance throughout the study.