Delivered-Dose Validation of Nonadaptive Diagnostic Computed Tomography-Based Volumetric Modulated Arc Therapy for Simulation-Free Palliative Radiation Therapy.

PURPOSE: Simulation-free radiation therapy (SFRT) using diagnostic computed tomography (dCT) may improve timeliness and reduce treatment burden in palliative care. We evaluated agreement between planned and delivered dose for nonadaptive dCT-based volumetric modulated arc therapy (VMAT) in palliative bone radiation therapy using cone beam CT (CBCT)-based dose recalculation. METHODS AND MATERIALS: In this single-center retrospective dosimetric study, 30 VMAT plans were generated from 26 imaging data sets obtained from a randomized SFRT trial cohort and clinical workflows. Patients had been treated clinically using field-based SFRT; data sets were retrospectively replanned with VMAT. Virtual planned dose (VPD) was calculated on dCT, and virtual delivered dose (VDD) was recalculated on first-fraction CBCT using identical beam parameters. The primary endpoint was relative planning target volume (PTV) D95 (dose received by 95% of the PTV), calculated as the VDD/VPD ratio and expressed as a percentage. Secondary endpoints included PTV V90 (percentage volume of the PTV receiving ≥90% of the prescription dose), hotspot metrics, and organ-at-risk dosimetry. RESULTS: Nineteen plans treated spinal targets, and 11 treated pelvic or proximal femoral targets. Relative PTV D95 showed excellent preservation of target coverage (mean, 99.6% ± 2.4%; median, 99.7% [IQR, 98.2%-100.7%]). All plans maintained a delivered PTV D95 ≥97% of the planned value. Relative PTV D95 did not differ by treatment site (P = .52). PTV V90 remained highly preserved (mean absolute change, -0.3%). Organ-at-risk metrics showed small absolute differences between VPD and VDD. Exploratory analyses demonstrated weak associations between Hounsfield unit differences and dosimetric variation, and homogeneous density sensitivity analyses showed similarly preserved target coverage. CONCLUSIONS: Nonadaptive dCT-based VMAT planning for palliative bone radiation therapy demonstrated high agreement between planned and CBCT-recalculated delivered dose. These findings support the implementation of VMAT-based SFRT using standard image guided radiation therapy workflows and existing linear accelerator infrastructure.