ESTRO 2023 - Abstract Book

S1696

Digital Posters

ESTRO 2023

The current CBCT protocol showed acceptable image quality, when excluding patients with a hip prosthesis. A generic planning template (single 360º VMAT arc) was developed for automated plan optimization. It uses multicriterial optimization to optimize OAR sparing. To accelerate optimization, the calculation grid was reduced from 3x3x3 mm ³ to 4x4x4 mm ³ . Test plans for two fractions in ten retrospective patients showed good target coverage with equal or improved OAR sparing compared to recalculation of the clinical plan. QA measurements of test plans showed good plan quality: mean gamma pass rate 99.5% (3%/3mm). Multiple workflow tests were completed successfully. The average workflow duration is shown in Fig. 2, indicating that with a maximum contouring time of 10 minutes, the workflow length stays below 25 minutes. Average plan optimization time is 3 minutes.

Different disciplines have been trained to perform the workflow. The workflow is RTT-led and supervised by a radiation oncologist. A medical physicist will be present during the first fractions. A pilot was started to show the feasibility of the workflow in three 10/13x3 Gy palliative bladder patients. Conclusion We developed and implemented an online adaptive CBCT-guided VMAT workflow for an Elekta Synergy CBCT-linac. As of October 2022, we started a pilot in which the workflow is our clinical procedure.

PO-1941 Feasibility of a focal boost in MRI-guided online adaptive SBRT for locally advanced prostate cancer

M. Dassen 1 , A. Betgen 1 , P. De Ruiter 1 , J. Van Der Linden 1 , L. Wiersema 1 , B. Neijndorff 1 , T. Janssen 1 , L. Abbenhuis 2 , P. Van Kollenburg 2 , C. Reijnen 2 , L. Kerkmeijer 2 , F. Pos 1 , U. Van Der Heide 1 , E. Brunenberg 2 1 The Netherlands Cancer Institute, Radiation Oncology, Amsterdam, The Netherlands; 2 Radboud University Medical Center, Radiation Oncology, Nijmegen, The Netherlands