Segmental Cardiac Radiation Dose Determines Magnitude of Regional Cardiac Dysfunction

BACKGROUND: Subclinical left ventricular dysfunction detected by 2‐dimensional global longitudinal strain post breast radiotherapy has been described in patients with breast cancer. We hypothesized that left ventricular dysfunction postradiotherapy may be site specific, based on differential segmental radiotherapy dose received. METHODS AND RESULTS: Transthoracic echocardiograms were performed at baseline, 6 weeks, and 12 months postradiotherapy on 61 chemotherapy‐naïve women with left‐sided breast cancer undergoing tangential breast radiotherapy. Radiation received within basal, mid, and apical regions for the 6 left ventricular walls was quantified from the radiotherapy treatment planning system. Anterior, anteroseptal, and anterolateral walls received the highest radiation doses, while inferolateral and inferior walls received the lowest. There was a progressive increase in the radiation dose received from basal to apical regions. At 6 weeks, the most significant percentage deterioration in strain was seen in the apical region, with greatest reductions in the anterior wall followed by the anteroseptal and anterolateral walls, with a similar pattern persisting at 12 months. There was a within‐patient dose–response association between the segment‐specific percentage deterioration in strain at 6 weeks and 12 months and the radiation dose received. CONCLUSIONS: Radiotherapy for left‐sided breast cancer causes differential segmental dysfunction, with myocardial segments that receive the highest radiation dose demonstrating greatest strain impairment. Percentage deterioration in strain observed 6 weeks postradiotherapy persisted at 12 months and demonstrated a dose–response relationship with radiotherapy dose received. Radiotherapy‐induced subclinical cardiac dysfunction is of importance because it could be additive to chemotherapy‐related cardiotoxicity in patients with breast cancer. Long‐term outcomes in patients with asymptomatic strain reduction require further investigation.