Growing evidence suggests that spatial dose variations across the rectal surface influence toxicity risk after radiotherapy. Existing methodologies employ a fixed, arbitrary physical extent for rectal dose mapping, limiting their analysis. We developed a method to standardise rectum contours, unfold them into 2D cylindrical surface maps, and identify subregions where higher doses increase rectal toxicities.
Data of 1,048 patients with prostate cancer from the REQUITE study were used. Deep learning based automatic segmentations were generated to ensure consistency. Rectum length was standardised using linear transformations superior and inferior to the prostate. The automatic contours were validated against the manual contours through contour variation assessment with cylindrical mapping. Voxel-based analysis of the dose surface maps for the manual and automatic contours against individual rectal toxicities was performed using Student's t permutation test and Cox Proportional Hazards Model (CPHM). Significance was defined by permutation testing.
Our method enabled the analysis of 1,048 patients using automatic segmentation. Student's t-test showed significance (p < 0.05) in the lower posterior for clinical-reported proctitis and patient-reported bowel urgency. Univariable CPHM identified a 3 % increased risk per Gy for clinician-reported proctitis and a 2 % increased risk per Gy for patient-reported bowel urgency in the lower posterior. No other endpoints were significant.
We developed a methodology that unfolds the rectum to a 2D surface map. The lower posterior was significant for clinician-reported proctitis and patient-reported bowel urgency, suggesting that reducing the dose in the region could decrease toxicity risk.
Physics and imaging in radiation oncology. 2025 Jan 20*** epublish ***
Artemis Bouzaki, Dylan Green, Marcel van Herk, Jane Shortall, Tanuj Puri, Sarah Kerns, David Azria, Marrie-Pierre Farcy-Jacquet, Jenny Chang-Claude, Ananya Choudhury, Alison Dunning, Maarten Lambrecht, Barbara Avuzzi, Dirk De Ruysscher, Petra Seibold, Elena Sperk, Christopher Talbot, Ana Vega, Liv Veldeman, Adam Webb, Barry Rosenstein, Catharine M West, Eliana Gioscio, Tiziana Rancati, Eliana Vasquez Osorio, Alan McWilliam
Division of Cancer Sciences, University of Manchester, Manchester, the United Kingdom of Great Britain and Northern Ireland., Department of Engineering Science, University of Oxford, Oxford, the United Kingdom of Great Britain and Northern Ireland., Medical College of Wisconsin, Milwaukee, WI, USA., Federation Universitaire d'Oncologie Radiothérapie d'Occitanie Méditerranée, Univ Montpellier, INSERM U1194 IRCM, Institut du Cancer Montpellier (ICM), Montpellier, France., Federation Universitaire d'Oncologie Radiothérapie d'Occitanie Méditerranée, Institut du Cancer Du Gard (ICG), CHU Carémeau, Nîmes, France., German Cancer Research Center (DKFZ), Division of Cancer Epidemiology, Heidelberg, Germany., Centre for Cancer Genetic Epidemiology, Strangeways Research Laboratory, University of Cambridge, Cambridge, the United Kingdom of Great Britain and Northern Ireland., KU Leuven, Leuven, Belgium., Department of Radiation Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy., Department of Radiation Oncology (Maastro), Maastricht University Medical Center, GROW School, Maastricht, the Netherlands., Department of Radiation Oncology, Universitätsmedizin Mannheim, Medical Faculty Mannheim, University of Heidelberg, Mannheim, Germany., Department of Genetics & Cancer Sciences, University of Leicester, the United Kingdom of Great Britain and Northern Ireland., Instituto de Investigación Sanitaria de Santiago de Compostela (IDIS), Santiago de Compostela, Spain., Ghent University Hospital, Belgium., Departments of Radiation Oncology & Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, NY, USA., Translational Radiobiology Group, Division of Cancer Sciences, University of Manchester, The Christie NHS Foundation Trust, Manchester, the United Kingdom of Great Britain and Northern Ireland., Data Science Unit, Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy.