Deployment of a Deep Learning Automated Cardiac Sub-Structure Contouring Algorithm to Measure Coronary Dose Exposure Trends in Lung Cancer Radiation Therapy

Abstract

Radiation dose exposure to the left anterior descending coronary artery (LAD) is associated with major adverse cardiac events (MACE) and all-cause mortality (ACM) after radiotherapy (RT) for locally-advanced non-small cell lung cancer (LA-NSCLC). Segmentation of cardiac sub-structures has not been routinely performed historically, and the purpose of the study was to deploy a deep learning (DL)-based automated cardiac sub-structure contouring algorithm to calculate LAD radiation dose exposure and understand temporal trends in a large population. We previously trained a DL algorithm to segment cardiac substructures, using research contours from 560 LA-NSCLC patients (pts), and validated the LAD auto-segmentation algorithm geometrically, dosimetrically and with outcomes. In this study, we deployed the DL algorithm to auto-segment the LAD and heart on planning CT scans in an independent cohort of 1708 consecutive LA-NSCLC pts treated at an academic center and 4 affiliated community centers from 2014-21. We calculated the LAD volume receiving 15 Gy (V15), and mean heart dose (MHD) using the DL contours and the treated plan. We analyzed the distribution of key dosimetric values for heart (LAD V15, MHD) and lung (V20, mean lung dose [MLD], V5) over time and used the Mann-Kendall statistical test for trend. The median prescribed dose was 50 Gy. 63% of patients were treated with intensity-modulated radiation therapy (IMRT) and 37% 3D-conformal (Table), with increasing IMRT use over time. The median lung V20, V5, MLD, and MHD did not significantly change over time (p>0.05). The median LAD V15 decreased significantly (p<0.05 for trend) in 2020-1, with significantly more cases achieving a V15<10% compared to prior years (p<0.05). The LAD distribution shift coincides with the 2020 publication of a study showing an association of V15<10% with decreased risk of MACE/ACM. DL-based auto-segmentation of cardiac substructures can be deployed at large-scale to study trends in dose exposure to newly identified critical organs-at-risk such as the LAD at the population level. Lowering LAD dose did not impact other cardiopulmonary constraints, but further work is needed to study impact on outcomes.