ESTRO 2023 - Abstract Book

S1586

Digital Posters

ESTRO 2023

PO-1848 Towards clinical application: Potential margin reduction in proton therapy with prompt-gamma imaging

S. Bertschi 1 , J. Berthold 1,2 , J. Pietsch 1,2 , J. Smeets 3 , G. Janssens 3 , K. Stützer 1,2 , C. Richter 1,2,4,5

1 OncoRay – National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden - Rossendorf, Dresden, Germany; 2 Helmholtz-Zentrum Dresden - Rossendorf, Institute of Radiooncology - OncoRay, Dresden, Germany; 3 Ion Beam Applications SA, Research, Louvain-la-Neuve, Belgium; 4 Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany; 5 German Cancer Consortium (DKTK), Partner Site Dresden, Germany and German Cancer Research Center (DKFZ), Heidelberg, Germany Purpose or Objective In proton therapy (PT), considerable clinical planning margins around the target are needed to account for various uncertainties. We provide the first estimation of their potential reduction when using prompt gamma imaging (PGI) for routine treatment verification and intervention in prostate cancer PT. Materials and Methods Three scenarios were investigated based on clinical PGI data of 10 prostate cancer patients treated with hypofractionated (3Gy/Fx) PBS (74 fractions/148 fields monitored). Scenario A describes the current clinically used margins during CTV-based robust treatment planning for (1) patient setup uncertainties and (2) dual-energy CT based range uncertainties of 2%+2mm. Scenario B estimates the potential margin reduction when using the current 2nd generation PGI system as trigger for an online adaptive proton therapy (OAPT) workflow. Hereby, a setup protocol using orthogonal X-ray imaging, immediate PGI analysis and, if necessary, online re-planning based on volumetric imaging, were assumed. To quantify the margin reduction potential, the accuracy of the current PGI system for a field-wise evaluation was estimated, considering only the statistical fluctuation (2 σ ) of the PGI information per field since the systematic uncertainty was previously shown to be negligible. In room CTs in treatment position, available for all 74 fractions, were used to calculate the PGI ground-truth. Furthermore, the current PGI data processing workflow was optimized to enable a semi-automated analysis (Fig. 1a). Scenario C describes further margin reduction for an OAPT workflow including initial volumetric imaging at isocenter and adaptation before irradiation. For an exemplary patient case, the benefit of the reduced margins was investigated by comparing the dose distributions of the clinical plan and the re-optimized plans with reduced margins.