LAUSR

Purpose: Online Adaptive Radiation Therapy(oART) follows a different treatment paradigm than conventional radiotherapy and, because of this, the resources, implementation, and workflows needed are unique. The purpose of this report is to outline our institution's experience establishing, organizing, and implementing an oART program using the Ethos therapy system. Methods: We include resources used; operational models utilized, program creation timelines, and our institutional experiences with implementation and operation of an oART program. Additionally, we provide a detailed summary of our first year's clinical experience where we delivered over 1000 daily adaptive fractions. For all treatments, the different stages of online adaption, primary patient set-up, initial kV-CBCT acquisition, contouring review and edit of influencer structures, target review and edits, plan evaluation and selection, Mobius3D 2nd check and adaptive QA, 2nd kV-CBCT for positional verification, treatment delivery, and patient leaving the room, were analyzed. Results: We retrospectively analyzed data from ninety-seven patients treated from August 2021-August 2022. 1677 individual fractions were treated and analyzed, 632(38%) were non-adaptive and 1045(62%) were adaptive. 74 of the 97 patients (76%) were treated with standard fractionation and 23 (24%) received stereotactic treatments. For the adaptive treatments, the generated adaptive plan was selected in 92% of treatments. On average({+/-}std), adaptive sessions took 34.52{+/-}11.42 minutes from start to finish. The entire adaptive process (from start of contour generation to verification CBCT), performed by the physicist (and physician on select days), was 19.84{+/-}8.21 minutes. Conclusion: We present our institution's experience establishing, organizing, and implementing an oART program using the Ethos therapy system. It took us 12 months from project inception to treatment of our first patient and 12 months to treat 1000 adaptive fractions. Retrospective analysis of delivered fractions showed that average overall treatment time was approximately 35 minutes and average time for the adaptive component of treatment was approximately 20 minutes.