Adaptive Radiotherapy for Safe Hypofractionation

This phase II, registry-based cohort-multiple randomized controlled trial (cmRCT) evaluates whether daily online adaptive radiotherapy (ART) enables the safe delivery of hypofractionated, iso-biologically equivalent (EQD2) external beam radiotherapy compared with standard-of-care (SOC) fractionation. Conventional radiotherapy requires generous planning target volume (PTV) margins to account for inter-fraction anatomical variation, which increases radiation exposure to surrounding organs at risk (OARs) and may contribute to toxicity. Modern ART platforms using daily on-table imaging (kV-CBCT or MRI guidance) allow real-time contour adaptation and online plan re-optimization based on same-day anatomy. This approach enables margin reduction while maintaining target coverage and may permit safe hypofractionation. Eligible patients enrolled in an institutional prospective registry will be randomized (1:1) to receive either SOC radiotherapy or hypofractionated ART across multiple pelvic disease strata (post-prostatectomy prostate cancer, intact prostate cancer, endometrial cancer, cervical cancer, and rectal cancer). The primary objective is to demonstrate non-inferiority of hypofractionated ART compared with SOC in terms of cumulative incidence of Grade ≥2 toxicity (CTCAE v5). Secondary outcomes include acute and late toxicity, oncologic outcomes (progression-free survival, locoregional failure, distant metastases, overall survival), patient-reported outcomes, treatment efficiency, and dosimetric parameters. A Bayesian monitoring framework with pre-specified safety and futility stopping rules will be used to ensure patient safety and clinical equipoise throughout the trial.