A probabilistic deep learning model of inter-fraction anatomical variations in radiotherapy

Oscar Pastor-Serrano*, Steven Habraken, Mischa Hoogeman, Danny Lathouwers, Dennis Schaart, Yusuke Nomura, Lei Xing, Zoltán Perkó

*Corresponding author for this work

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Abstract

Objective. In radiotherapy, the internal movement of organs between treatment sessions causes errors in the final radiation dose delivery. To assess the need for adaptation, motion models can be used to simulate dominant motion patterns and assess anatomical robustness before delivery. Traditionally, such models are based on principal component analysis (PCA) and are either patient-specific (requiring several scans per patient) or population-based, applying the same set of deformations to all patients. We present a hybrid approach which, based on population data, allows to predict patient-specific inter-fraction variations for an individual patient. Approach. We propose a deep learning probabilistic framework that generates deformation vector fields warping a patient's planning computed tomography (CT) into possible patient-specific anatomies. This daily anatomy model (DAM) uses few random variables capturing groups of correlated movements. Given a new planning CT, DAM estimates the joint distribution over the variables, with each sample from the distribution corresponding to a different deformation. We train our model using dataset of 312 CT pairs with prostate, bladder, and rectum delineations from 38 prostate cancer patients. For 2 additional patients (22 CTs), we compute the contour overlap between real and generated images, and compare the sampled and ‘ground truth’ distributions of volume and center of mass changes. Results. With a DICE score of 0.86 ± 0.05 and a distance between prostate contours of 1.09 ± 0.93 mm, DAM matches and improves upon previously published PCA-based models, using as few as 8 latent variables. The overlap between distributions further indicates that DAM’s sampled movements match the range and frequency of clinically observed daily changes on repeat CTs. Significance. Conditioned only on planning CT values and organ contours of a new patient without any pre-processing, DAM can accurately deformations seen during following treatment sessions, enabling anatomically robust treatment planning and robustness evaluation against inter-fraction anatomical changes.

Original languageEnglish
Article number085018
JournalPhysics in Medicine and Biology
Volume68
Issue number8
DOIs
Publication statusPublished - 10 Apr 2023

Bibliographical note

Acknowledgments:
This work is supported by KWF Kanker Bestrijding [Grant Number 11711] and is part of the KWF research project PAREL. Zoltán Perkó would like to thank the support of the NWO VENI grant ALLEGRO (016.Veni.198.055) during the time of this study. We would like to thank Haukeland University Hospital (Bergen, Norway), responsible oncologist Svein Inge Helle, physicist Liv Bolstad Hysing and Dr Jeffrey Siebers for providing the CT-data with contours. Lei Xing wishes to acknowledge the supports of the National Institutes of Health (NIH) (1R01CA223667, 1R01CA176553, and 1R01CA227713) and Varian Medical Systems (Palo Alto, CA).

Publisher Copyright: © 2023 The Author(s). Published on behalf of Institute of Physics and Engineering in Medicine by IOP Publishing Ltd.

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