Time trends in cardiac doses in 10,000 patients receiving curative thoracic radiation therapy between 2009 and 2020

Background and purpose In the last 20 years, it has become well-documented that incidental cardiac exposure to ionizing radiation is associated with a clinically relevant increased risk of cardiovascular morbidity. In parallel, radiation therapy technologies have been developed to provide target dose coverage with less exposure to adjacent organs at risk. In the current work, we investigate trends in cardiac exposure among patients treated with curative intent radiotherapy from a single institution between 2009 to 2020. Materials and methods 10,215 treatment courses were analyzed from 9,966 patients treated with curative intent for intrathoracic or breast cancers in the period 2009-2020. All hearts were re-delineated using an AI model to ensure consistency over time. Cardiac doses were extracted in 3D from the record-and-verify system and converted, voxel-by-voxel, to equi-effective doses in 2 Gy fractions (EQD2) using α/β=2 Gy. Mean heart dose (in EQD2) and volume exposed to 5 and 40 Gy (V5 and V40Gy), respectively, were extracted. Time trends in these cardiac dose-volume metrics were investigated for each diagnosis. Results Patients with esophageal cancer had the highest mean heart dose (median = 11.67 Gy; IQR = 2.85, 18.18), while the lowest was observed in patients with breast cancer (median = 0.60 Gy; IQR = 0.30, 1.08) and lymphoma (median = 0.01 Gy; IQR = 0.00, 0.38). A decreasing trend over time was seen most clearly for patients with esophageal and lung cancers (p<0.05). Among patients with breast cancer, V40 decreased from 2009-2015 after which we observed an increase. Conclusion There has been a significant reduction in radiation exposure to the heart in patients treated in the period 2009-2020, likely due to increased awareness of cardiovascular toxicity and technological developments. The study also found a significant increase in V40 from 2015 to 2020 for patients with breast cancers, possibly related to increased prioritization of target coverage. Highlights 10,215 radiation therapy plans extracted and analyzed Hearts were re-delineated with machine learning on the therapy CT-scan to ensure time-independent delineations Cardiac doses were found to decrease over time, especially high dose exposure of intrathoracic lesions An unexpected increase in cardiac high dose volume (V40Gy) for breast cancer treatment plans in recent years was observed