ESTRO 2022 - Abstract Book

S837

Abstract book

ESTRO 2022

Conclusion On average, AF provided only a small increase in tumor BED. However, AF may yield substantial benefits for individual patients with large variations in the geometry.

OC-0945 Treatment verification with prompt-gamma imaging: Detection sensitivity of anatomical changes in HNC

J. Berthold 1,2 , L. Hübinger 1,3 , N. Piplack 1,4 , J. Pietsch 1,2 , C. Khamfongkhruea 1,5 , J. Thiele 6 , S. Appold 6 , E. Traneus 7 , G. Janssens 8 , J. Smeets 8 , K. Stützer 1,2 , C. Richter 1,2,6,9 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 Faculty of Physics, Technische Universität Dresden, Dresden, Germany; 4 Faculty of Electrical and Computer Engineering , Technische Universität Dresden, Dresden, Germany; 5 Princess Srisavangavadhana College of Medicine, Chulabhorn Royal Academy, Bangkok, Thailand; 6 Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany; 7 RaySearch Laboratories AB, Research, Stockholm, Sweden; 8 Ion Beam Applications SA, Research, Louvain-la-Neuve, Belgium; 9 German Cancer Consortium (DKTK), partner site Dresden, Germany and German Cancer Research Center (DKFZ), Heidelberg, Germany Purpose or Objective In this systematic study, we investigate the sensitivity of prompt-gamma imaging (PGI) towards the field-wise detection of inter-fractional anatomical changes in proton therapy (PT) of head and neck cancer (HNC) patients. Materials and Methods Spot-wise range shifts ∆ R PGI were monitored with a PGI-slit-camera during 22 field deliveries of HNC pencil beam scanning (PBS) treatments of 4 patients (field-wise dose per fraction: 0.7-1.0GyE). In-room CTs were acquired for all monitored fractions and range shifts ∆ R IDD at the 80% falloff of spot-wise integrated depth-dose (IDD) profiles served as input for an automatic field-wise ground truth classification (Fig.1). To receive results consistent with an additional manual dose-based classification per field, a PBS spot with relative weight to the field >0.1% was rated as relevant if | ∆ R IDD | was ≥ 5mm for that and at least 1 neighboring spot. Subsequently, a field was classified as relevantly changed if at least 1.5% of all spots were rated relevant . For the independent PGI evaluation, spots were clustered based on Bragg-peak position and proton number to mitigate statistical measurement uncertainty. Clusters with | ∆ R PGI | ≥ 5mm were classified as relevant . For training of the field-wise PGI classification model, the number of relevant clusters, that is necessary to classify the whole field as relevantly changed , was optimized with respect to the IDD ground truth classification using a training set of 11 fields. Finally, the classification model was validated on an independent test set (11 fields).