Radiation dose and cardiac risk in breast cancer treatment: An analysis of modern radiation therapy including community settings.

PURPOSE Adjuvant radiation therapy (RT) for breast cancer improves outcomes, but prior studies have documented substantive cardiac dose and cardiac risk. We assessed the mean heart dose (MHD) of RT and estimated the risk of RT-associated cardiac toxicity in women undergoing adjuvant RT for breast cancer in contemporary (predominantly) community practice. METHODS AND MATERIALS We identified women with left-sided breast cancer receiving adjuvant RT between 2012 and 2014 from 94 centers across 16 states. We used bivariate analyses and multivariable linear regression to assess associations between RT techniques and MHD. Excess RT-related cardiac risk by age 80 was estimated for women diagnosed at age 60 using the previously reported relationship between MHD and cardiac risk. RESULTS Among 1161 women, 77.3% were treated in community practice and with breast conservation (77.8%). The most common techniques were free-breathing (92.2%), supine (94.8%), and fixed gantry intensity modulated RT (FG-IMRT; 46.9%). The median MHD was 2.76 Gy (interquartile range, 1.47-5.03). In multivariable analyses, the predicted median MHD with deep inspiration breath hold was 2.41 Gy compared with 3.86 Gy with free-breathing (P < .001). Three-dimensional conformal RT (3D-CRT) was associated with a lower predicted median MHD (2.78 Gy) than FG-IMRT (4.02 Gy) or rotational IMRT, 6.60 Gy, P < .001). For 60-year-old women with the median MHD of the study population (2.76 Gy) and no cardiovascular risk factors, the 20-year predicted excess risk of death from ischemic heart disease attributable to radiation was 3.5 excess events/1000 patients, in contrast to estimates of 8 events/1000 from prior analyses. The predicted risk of cardiac events varied based on radiation technique, with 4 excess events/1000 with 3D-CRT, 5 excess events/1000 with FG-IMRT, and 8 excess events/1000 with rotational IMRT. CONCLUSIONS MHD varies substantially across patients and is influenced by technique in predominantly community settings. Overall risk of cardiac toxicity is modest.