The aim of this study is to evaluate the efficacy and safety of hypofractionated simultaneous integrated boost volumetric arc radiation therapy (SIB - VMAT) for high-risk and very high-risk localized prostate cancer in terms of:

1. Acute and late gastrointestinal and genitourinary toxicities.
2. Evaluate the efficacy in terms of early bPFS.
3. Dosimetric evaluation in terms of target coverage and organs at risk sparing

Background:

Despite the overwhelming success of hypofractionation for prostate-only radiotherapy, a substantial gap in high-level evidence exists regarding its application to elective pelvic lymph node irradiation. The pivotal trials establishing the 60 Gy/20 fraction standard (such as CHHiP and PROFIT) largely excluded extensive whole pelvic nodal irradiation. Consequently, there remains a lack of definitive, prospective data validating the safety and efficacy of a hypofractionated Simultaneous Integrated Boost (SIB) technique that concurrently delivers 44 Gy to the pelvic lymph nodes and 60 Gy to the prostate over 20 fractions. While modern image-guided, Volumetric Modulated Arc Therapy (VMAT) provides the dosimetric conformity required to spare organs at risk (OARs) such as the bladder and bowel, clinical confirmation of acute and late toxicities in the context of wide-field pelvic irradiation remains paramount.

Therefore, this prospective, single-arm trial is designed to address this critical evidence gap. By rigorously evaluating the GI and GU toxicity profiles and early biochemical control, this study seeks to validate the 4-week SIB protocol as a safe, efficacious, and resource-efficient standard of care for high-risk prostate cancer requiring elective pelvic nodal irradiation.

Objectives:

To evaluate the safety of hypofractionated SIB - VMAT radiation therapy in terms of acute and late GI and GU toxicities, and also evaluate the efficacy in terms of early bPFS, and lastly, dosimetric evaluation in terms of target coverage and OAR sparing Study Arms Single arm Population: Histologically confirmed localized prostatic adenocarcinoma with high and very high risk groups.

Primary Endpoint: Acute and late GIT & GU toxicities (according to CTCAE & RTOG).

Secondary Endpoints:

1. To evaluate early biochemical control (serum PSA) at 6 and 12 months.
2. To perform a dosimetric analysis of target coverage and of organs at risk (OARs) dose contains.

Significance α = 0.05 two-sided; power = 80%; minimum detectable HR = 0.65 Duration 12 months total (from IRB approval to submission of the manuscript).

Inclusion Criteria:

• Histologically confirmed adenocarcinoma of the prostate.
• Classification as High-Risk (HR) or Very High-Risk (VHR) per NCCN guidelines (e.g., T3a+, PSA > 20 ng/mL, or Gleason Score 8-10).
• Adequate baseline urinary function (IPSS \le 20).
• Multiparametric MRI of the prostate.
• CT Chest, Abdomen, and Pelvis.
• Bone scan
• Optional: PSMA-PET/CT to definitively exclude distant metastases (M1) and provide high-fidelity nodal assessment prior to treatment planning.

Exclusion Criteria:

• Prior pelvic radiotherapy.
• History of Inflammatory Bowel Disease (IBD) or active severe proctitis.
• Presence of distant metastases.