A Phantom-Based Evaluation of Direct to Unit Adaptive Radiotherapy on an Adaptive Linac
Abstract
Purpose
Direct-to-unit (DTU) adaptive radiation therapy (ART) is an emerging workflow that reduces treatment delays for urgent radiation therapy by eliminating the need for a separate simulation scan. Despite increasing clinical adoption, standardized commissioning guidance for simulation-free workflows remains limited. This study presents a commissioning framework for DTU ART to support reproducible clinical implementation.
Methods
An American College of Radiology (ACR) phantom was scanned on a Siemens Flash CT with an iterative reconstruction algorithm and on a Varian Ethos 2.0 system using three CBCT reconstruction
Methods
iCBCT Acuros, iCBCT Acuros with metal artifact reduction (MAR), and FeldKamp Davis Kress (FDK). The diagnostic CT dataset was used to generate baseline treatment plans, which were recalculated and re-optimized on each CBCT dataset to simulate a DTU adaptive workflow. Dose-volume metrics were extracted for the PTV and PTV_Eval (PTV excluding OARs+5mm) and compared across image sets. Statistical analysis included paired t-tests and two one-sided tests (TOST) for equivalence on D95%, D2%, V95%Rx, Dmean, Dmin, and Dmax. Gamma analysis with 2%/2mm (global and 10% threshold) was performed between the DxCT plan and the re-calculated plan on each imaging protocol.
Results
Using a ±30 HU equivalence bound, TOST showed iCBCT Acuros and iMAR were equivalent to DxCT (p-value TOST=0.0084 and 0.0115), whereas FDK was not (p-value TOST=0.115). Paired t-tests showed statistically significant differences for some dosimetry metrics (p 96%), demonstrating high similarity in dose distribution.
Conclusion
DTU ART can be commissioned using CBCT-based dose calculation on the Ethos 2.0 system. This framework provides a practical and reproducible approach for validating DTU workflows while maintaining dosimetric accuracy and patient safety.