ESTRO 2021 Abstract Book

S743

ESTRO 2021

Conclusion An accurate BDT prediction and delivery sequence model was established for a cyclotron proton therapy system, IBA ProteusPLUS®. Based on these findings, a machine-specific delivery sequence is highly recommended to evaluate the interplay effect in mobile target treatment accurately. Most of the institutions could adopt this experimental method to model their own specific proton system. PD-0903 Gel dosimetry-based range evaluation as quality assurance tool for adaptive proton radiotherapy S. Neppl 1,2,3 , C. Kurz 1,4 , D. Köpl 5 , I. Yohannes 6 , M. Schneider 7 , D. Bondesson 7 , M. Rabe 1 , C. Belka 1,8 , O. Dietrich 7 , G. Landry 1,4 , K. Parodi 2 , F. Kamp 1,3 1 University Hospital, LMU Munich, Department of Radiation Oncology, Munich, Germany; 2 Ludwig- Maximilians-Universität München (LMU Munich), Department of Medical Physics, Garching bei München, Germany; 3 University Hospital Cologne, University of Cologne, Department of Radiation Oncology and Cyberknife Center, Cologne, Germany; 4 Ludwig-Maximilians-Universität München (LMU Munich), Department of Medical Physics, Munich, Germany; 5 Rinecker Proton Therapy Center, Medical Physics, Munich, Germany; 6 Rinecker Proton Therapy Center, Medical Physics, Munich, Germany; 7 University Hospital, LMU Munich, Department of Radiology, Munich, Germany; 8 German Cancer Consortium (DKTK), Partner site Munich, Munich, Germany Purpose or Objective The implementation of volumetric in-room imaging for online adaptive proton radiotherapy makes extensive testing of image intensity accuracy for treatment plan optimization necessary. Current evaluation approaches mainly focus on recalculation of the original plans on the new images, lacking experimental verification, and ignoring the impact of the plan re-optimization process. In this study 3D printed head phantoms with gel and film inserts were used to analyze the influence of in-room image quality on dose optimization and calculation. The specific case of intensity-corrected CBCTs (scCBCT) was studied. Proton ranges were used as a sensitive tool to probe image intensity deviations. Materials and Methods