Abstract P1-10-12: AI-based cardiac sub-structures segmentation for safer radiotherapy planning
Authors: Loap Pierre , Botticella Angela , De Marzi Ludovic , Levy Antonin , Bolle Stephanie , COLAME Stéphane , Cannard Arthus , Martineau-Huynh Catherine , Oumani Ayoub , Roque Thais S. , Paragios Nikos , Deutsch Eric , Luo Caroline , Kirova Youlia M. , Rivera Sofia 
Published: March 2023

Abstract
Purpose: Whilst radiotherapy increases cure rates in breast cancer, lung cancer, among others, it may also involve some cardiac exposure, which in turn may increase the risk of different heart diseases. The heart is a complex anatomical organ that involves many different structures making it difficult to contour cardiac sub-structures reproducibly. Contouring, especially for these cases, suffers from inter- and intra-expert variability while being time consuming. Cardiac atlases have been developed to aid in the delineation of cardiac substructures. However, these methods have many shortcomings, including the inability to overcome variations in patient anatomy. In this study, a deep learning based commercial solution for automatic OAR delineation was trained following international guidelines for heart substructures delineation and tested on an unseen cohort of lung and breast patients to evaluate its clinical acceptability.
Methods: ART-Net, a CE-marked, FDA-cleared anatomically preserving deep-learning ensemble architecture for automatic annotation of OAR was evaluated using data of 20 breast/lung patients from 2 centers. Automatic annotation of 27 different structures (Ventricles (left and right), atria (left and right), left ventricle (anterior, apical, inferior, lateral, septal), LAD coronary (mid, proximal, distal, total), circumflex coronary (distal, proximal, total), RCA (distal, mid, proximal, total), coronary sinus, left main coronary artery, ascending aorta, pulmonary arteries, vena cava inferior, vena cava superior and the heart) was performed and submitted to 2 experts across 2 centers for qualitative evaluation. Contours were scored as A/acceptable, B/acceptable after minor corrections, and C/not acceptable for clinical use. To avoid any bias, experts were blind to whether the contour were manually, or AI delineated. The DSC between automatic and manual (ground truth) contours of the heart sub-structures were evaluated and compared with interobserver variability from the literature [1,2] using average and min DSC scores.
Results: Automatic contours were generated in a mean time of 0.5s per scan slice. Out of the 27 structures, 20 were considered clinically acceptable in the qualitative study. In the inter-expert variability study, 12 structures passed the test successfully using initial acceptance criterion over an acceptable sample size and 9 other structures demonstrated performances above the minimal threshold of inter-expert variability, sometimes on smaller datasets due to lack of manual data. Overall, 16 structures were included in the final model. 13 structures were considered clinically acceptable in 100% of the cases with AI contours rated at the same level as manual contours. For the other 3 structures (coronary sinus, left main coronary artery and vena cava inferior), the performance of the AI contours was slightly below that of the manual contours (within 3.4% difference), with the least performing structure being the coronary sinus (84% for AI vs 87% manual).
Conclusion: We show first results for the evaluation of AI-based auto-contouring tool for annotation of the substructures of the heart. The results show very good clinical acceptance, highlighting the high usability of the commercial tool for cardiac cases and its clinical implementation feasibility. The use of this AI tool can facilitate and accelerate future research studies investigating relationships between substructure doses and cardiac outcomes. Future work will include improvement of the sub-structures (mid, proximal, distal) and a retrospective meta-analysis to assess heart sub-structures degree of importance in terms of toxicity.
References:
1. Lee J., et al. Development of delineation for the left anterior descending coronary artery region in left breast cancer radiotherapy: An optimized organ at risk. Radiother Oncol. 2017
2. Duane F, et al. A cardiac contouring atlas for radiotherapy. Radiother Oncol. 2017
Table 1. Quantitative and qualitative results of the evaluation.
Heart sub-structures evaluated quantitatively with mean DSC compared to a range of DSC found in international guidelines and qualitatively as A or B (i.e. considered clinically acceptable). Highlighted are all structures that met the acceptance criterion of reaching a percentage of at least 85% of A or B, or that fell within the DICE range of interobserver variability found in the literature.
Citation Format: Pierre Loap, Angela Botticella, Ludovic De Marzi, Antonin Levy, Stephanie Bolle, Stéphane COLAME, Arthus Cannard, Catherine Martineau-Huynh, Ayoub Oumani, Thais S. Roque, Nikos Paragios, Eric Deutsch, Caroline Luo, Youlia M. Kirova, Sofia Rivera. AI-based cardiac sub-structures segmentation for safer radiotherapy planning [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-10-12.