ESTRO 2023 - Abstract Book

S1799

Digital Posters

ESTRO 2023

1 The University of Manchester, Division of Cancer Sciences, School of Medical Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Christie NHS Foundation Trust Hospital, Manchester, United Kingdom; 2 Mahidol University, Division of Radiation Oncology, Department of Radiology, Faculty of Medicine Siriraj Hospital, Bangkok, Thailand; 3 Université Montpellier, Department of Radiation Oncology, Montpellier Cancer Institute, Montpellier, France; 4 Vall d'Hebron Institute of Oncology, Hereditary Cancer Genetics Group, Vall d'Hebron Barcelona Hospital Campus, Barcelona, Spain; 5 KU Leuven, Department of Radiation Oncology, Leuven, Belgium; 6 Fondazione IRCCS Istituto Nazionale dei Tumori, Prostate Cancer Program, Milan, Italy; 7 Icahn School of Medicine at Mount Sinai, Department of Radiation Oncology, Department of Genetics and Genomic Sciences, New York, USA; 8 Maastricht University Medical Center, Department of Radiation Oncology (Maastro Clinic), GROW School for Oncology and Developmental Biology, Maastricht, The Netherlands; 9 University of Heidelberg, Department of Radiation Oncology, Universitätsklinikum Mannheim, Medical Faculty Mannheim, Mannheim, Germany; 10 University of Leicester, Leicester Cancer Research Centre, Leicester, United Kingdom; 11 Ghent University Hospital, Department of Radiation Oncology, Ghent, Belgium; 12 Instituto de Investigación Sanitaria de Santiago de Compostela, Fundación Pública Galega de Medicina Xenómica, Grupo de Medicina Xenómica (USC), Biomedical Network on Rare Diseases (CIBERER), Santiago de Compostela, Spain; 13 University Medical Center Hamburg- Eppendorf, University Cancer Center Hamburg, Hamburg, Germany; 14 German Cancer Research Center (DKFZ), Division of Cancer Epidemiology, Heidelberg, Germany; 15 Vall d'Hebron Hospital Universitari, Medical Physics Department, Vall d'Hebron Barcelona Hospital Campus, Barcelona, Spain Purpose or Objective In breast radiotherapy, electron boosts are often manually computed (e.g. by calculating monitor units based on target depth), which limits the analysis of relationships between dose distributions and outcomes. This study investigated the feasibility of reconstructing the dose distributions from manually-planned electron boosts in patients treated with breast- conserving radiotherapy as part of the REQUITE study (www.requite.eu). Materials and Methods In the REQUITE dataset, out of 198 patients treated with sequential electron boosts, only 72 had complete stored dose distributions (primary + boost). For the remaining 126, data available included: beam energy (MeV), boost prescription dose (Gy), CT and dose distribution for primary treatment. Data from 50 patients with complete stored dose distributions were used to develop and validate our dose reconstruction method. First, 10 cases were used to determine the best parameters for Monte-Carlo based electron dose reconstruction on Raystation (V11B) considering the following: a) the CT calibration curve, b) the number of histories, and c) the resolution of the dose calculation grid. A sensitivity analysis was performed to quantify the impact of varying those parameters using a Friedman test on SPSS v.28. Then, a validation set of 40 cases were used to quantify the accuracy of the reconstructed dose distributions. Figure 1 shows the workflow for electron dose reconstruction. The similarity between the reconstructed and stored dose distributions was evaluated using 3D-gamma index (3%3mm criteria), and dose metrics (D2%, D95%, and Dmean) extracted from breast and tumour bed contours. To evaluate the location of dose difference a dose-location histogram (DLH), as implemented in A Computational Environment for Radiological Research (CERR) was used.