Initial experience of clinical implementation of an Online Simulation-free CBCT-based Adaptive Radiotherapy (OSCAR) workflow for palliative and urgent treatment indications.

Abstract

BackgroundThe current standard radiotherapy treatment planning workflow typically requires several hours to days, during which patients must wait before treatment can be initiated. In certain oncological situations, however, treatment should commence as soon as possible. This is particularly critical in oncological emergencies to prevent further complications, as well as in palliative treatment indications where rapid symptom relief is essential.PurposeIn this study, we report our initial clinical experience with the online simulation-free CBCT-based adaptive radiotherapy (OSCAR) workflow, focusing on feasibility, workflow timing, and dosimetric plan quality.MethodsSeven anatomical regions were predefined for rapid treatment initiation using standardized RT intent templates in Ethos (Varian Medical Systems) with HyperSight CBCT. The OSCAR workflow was implemented including institutional safety strategies and alternative workflows where necessary. For the first patients treated with OSCAR, workflow timing was assessed, post-adaptive treatment strategies were documented, and Ethos on-couch IMRT plans were compared dosimetrically to corresponding IGRT VMAT plans generated in Eclipse on the HyperSight CBCT.ResultsThe OSCAR workflow was successfully established for the first 11 patients requiring rapid initiation of radiotherapy. The average total time required to initiate treatment was approximately 1 h and 50 min, while the adaptive treatment fraction (including patient setup, online adaptation, and irradiation) required approximately 20 min. The dosimetric comparison between static gantry IMRT and VMAT plans demonstrated that both techniques met clinical acceptance criteria for target coverage and OAR sparing.ConclusionsThe OSCAR workflow presented here enables rapid and clinically feasible treatment initiation without the need for a dedicated planning CT by combining standardized RT intent templates with HyperSight-CBCT-based online adaptation. While evaluated in a limited initial cohort and heterogeneous indications, the workflow demonstrated practicability and clinically acceptable plan quality. Future studies should evaluate scalability to additional disease sites and fractionation schemes, including ultra-hypofractionated regimens.