Long‐term cardiac outcomes in breast cancer patients treated with helical tomotherapy: Evaluating the applicability of 3D‐based dose constraints for intensity modulated radiation therapy

AbstractAdjuvant breast radiotherapy has been associated with cardiac toxicity due to older 2D and 3D techniques, with a linear relationship between mean heart dose (MHD) and ischemic cardiac events. Cardiac dose distribution differs with modern techniques like intensity‐modulated radiotherapy (IMRT), potentially affecting this relationship. This study evaluates long‐term cardiac toxicity in breast cancer patients treated with tomotherapy to reassess 3D‐derived dose constraints. Breast cancer patients treated with tomotherapy at Institut Curie from August 2010 to December 2015 were included. Patients had undergone breast‐conserving surgery or mastectomy, with some receiving chemotherapy or trastuzumab. Tomotherapy was used for anatomically challenging cases. The primary endpoint was cardiac toxicity correlated with MHD; secondary endpoints were overall and disease‐specific survival. Statistical analyses included logistic regression and Cox models. Among 179 patients, the median MHD was 7.04 Gy, with 95.6% having an MHD above 5 Gy. Sixty‐six patients had cardiovascular risk factors, and 28.5% were obese. Over a median follow‐up of 9.1 years, eight patients (4.5%) experienced cardiovascular events—all with pre‐existing risks or obesity. No significant correlation was found between MHD and major coronary events (p = 0.607) or heart failure (p = 0.800). Cardiac mortality was absent, and 10‐year overall and disease‐specific survival were 88.0% and 94.3%, respectively. Cardiac events in patients treated with tomotherapy were rare and driven by pre‐existing risk factors. The linear MHD‐toxicity relationship observed in 3D radiotherapy may not apply to IMRT, potentially leading to overestimated risks. Long‐term studies are needed to refine IMRT dose constraints.