ESTRO 2023 - Abstract Book

S191

Saturday 13 May

ESTRO 2023

Proffered Papers: Education and training / Professional development

OC-0254 Feasibility of RTT-only Conebeam CT-guided online adaptive radiotherapy for bladder cancer K. Goudschaal 1 , S. Azzarouali 1,2 , D. den Boer 2 , J. Visser 2 , L. Daniels 1,2 , M. Hulshof 1 , A. Bel 1 1 Amsterdam UMC location University of Amsterdam, Radiation Oncology, Amsterdam, The Netherlands; 2 Cancer Center Amsterdam, Cancer Therapy, Treatment and Quality of life, Amsterdam, The Netherlands Purpose or Objective Treating patients with muscle invasive bladder cancer is challenging due to interfraction variation in bladder filling. Online adaptive radiotherapy (oART) adapts to this daily anatomy change and minimizes dose to organs at risk (OAR) without compromising target coverage. Adapting the treatment to the daily GTV and OAR by Radiation Oncologist (RO) and Medical Physics Expert (MPE) is difficult because of limited time to work at the linac due to other activities in the department. The aim of this study was to investigate the feasibility of autonomously performing a Radiation Therapist (RTT)-only workflow of Conebeam CT (CBCT)-guided oART in terms of training and testing, tools and multidisciplinary communication. Materials and Methods Bladder cancer patients are treated with oART in 20 fractions on a ring-based linac integrated with CBCT and software platform for both treatment planning and delivery (Ethos, Varian, USA). Initially, from April 2021, 16 patients were treated by specialized RTTs under supervision of RO and MPE. In a second stage, the focus of this study starting March 2022, 10 patients were treated with an RTT-only workflow. To perform oART RTTs were trained about bladder target definition, practiced GTV, CTV and OAR delineation and performed oART in a simulation environment, under supervision of RO and MPE. A traffic light (Fig. 1) was used as a tool to safeguard various steps of oART in the RTT-only workflow. The training was then followed by a multidisciplinary test. Preceding the first fraction of each patient a multidisciplinary briefing was held with RO, MPE and RTTs, discussing patient specific details target volume and treatment planning. RO and MPE remained present during the first fraction. Within the RTT-only workflow fraction 2-20 were performed by RTTs only with RO and MPE available on call (remote or live). The oncology information system (OIS) was used for multidisciplinary communication about oART within the RTT-only workflow. RTT contacted RO and/or MPE in case of deviations in image quality, oART review, secondary dose calculation and IGRT steps. RO evaluated target coverage offline in week 1 and an expert RTT in week 2-4. MPE evaluated dosimetry randomly during the sessions and retrospectively.

Results Eighteen RTTs were trained and successfully completed the test.

RO and MPE were directly contacted in 23 of the remaining 189 fractions (Fig. 2A). The presence of RO and/or MPE during the RTT-only workflow was 17% (Fig. 2B). Outcome of offline target coverage by RO (12 of 187 fractions) and regarding dosimetry by MPE (13 of 200 fractions) was fed back to the RTT in the OIS as comment to confirm steps taken. If necessary, the RTT was contacted to adjust steps immediately (3 of 187 fractions) (Fig. 2C).