A roadmap for implementation of kV-CBCT online adaptive radiation therapy and initial first year experiences

Abstract

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.

Physicists should perform reference planning for CBCT guided online adaptive radiotherapy

“…Intent reviews could be implemented in the planning workflow to ensure adequate preparation prior to plan optimization within the IOE. 8 We agree that the planning techniques and optimization tools utilized within the IOE differ significantly from those in traditional TPS. However, our perspective maintains that the duty to impart knowledge and expertise to dosimetrists lies with the medical physicist, rather than assuming the role of primary planners.…”

“…could be performed prior to planning commencement to prevent any delays. Intent reviews could be implemented in the planning workflow to ensure adequate preparation prior to plan optimization within the IOE 8 …”

ACR benchmark testing of a novel high‐speed ring‐gantry linac kV‐CBCT system

“… 4 Currently, linear accelerator (linac) based CBCT imaging is utilized predominantly for daily patient positioning and for increased soft tissue and organ variation analysis compared to traditional kV or MV portal imaging 2 ; however, the use of adaptive radiation therapy has recently expanded. The current integration of CBCT into adaptive radiotherapy has been primarily through either manual HU overrides within regions of large HU differences between the planning CT and daily CBCT imaging, 9 synthetic CT generation from CBCT images, 10 , 11 , 12 or through deformable registration of the planning CT onto the CBCT. 4 , 13 At this time, there is no CBCT‐based imaging system that has image quality rivaling that produced by traditional diagnostic CT simulators, and CBCT systems are not able to be used for accurate dose calculations alone without a corresponding CT simulator image.…”

Evaluation and correlation of patient movement during online adaptive radiotherapy with CBCT and a surface imaging system

“…With the clinical implementation of kV‐CBCT‐based daily online‐adaptive radiotherapy, the ability to monitor, quantify, and correct patient movement during adaptive sessions is paramount. Online adaptive therapy corrects for daily variations in patient set‐up and anatomy by generating a new radiotherapy treatment plan using daily imaging to update structure contours 1–7 . Patients are kept in the treatment position for the entire adaptive session, which typically lasts between 20−45 min, leading to an increased likelihood of patient motion 7 .…”

“…Online adaptive therapy corrects for daily variations in patient set‐up and anatomy by generating a new radiotherapy treatment plan using daily imaging to update structure contours 1–7 . Patients are kept in the treatment position for the entire adaptive session, which typically lasts between 20−45 min, leading to an increased likelihood of patient motion 7 . Typically, radiographic imaging is repeated prior to treatment to verify the integrity of the patient setup and acceptability of anatomical changes (e.g.…”