Coronary Calcium Burden in Breast Cancer Patients Receiving Adjuvant Radiation Therapy

Abstract

Coronary artery calcium (CAC) score had been reported as an important imaging predictor for coronary artery disease (CAD). Even today, tangential radiotherapy (RT) in left-sided breast cancer (BC) still harbored potential harm to the heart, especially to the left anterior descending coronary artery. Previous studies took the mean heart dose as a surrogate of RT-associated cardiac toxicity, but no data were available on the radiation dose of each coronary artery. We aimed to explore the relation of CAC score and coronary radiation doses in BC patients treated with adjuvant RT. Additionally, we would like to examine the impact of other risk factors of CAD on the increment of coronary calcium burden. We retrospectively reviewed 146 BC female patients (median age at RT 50.5 years [range 24–82], median follow-up time 6.3 years [range 0.3–10.7]), treated with complete course of adjuvant RT in our institution from 2002 to 2010. All patients had received tangent field RT of 50 Gy at least to the breast or chest wall. We retrieved the following data by reviewing medical records: age, risk factors of CAD (diabetes, hypertension, hyperlipidemia, body mass index≧25), and treatment-related profiles. Pre-RT and post-RT computed tomography (CT) scans were obtained, and all CT scans were evaluated by an experienced cardiovascular radiologist in determining the absolute CAC scores of the left main artery (LM), left anterior descending coronary artery (LAD), left circumflex artery (LCX), and right coronary artery (RCA). The annual increment of CAC (CACinc) was calculated by dividing the difference of pre-RT and post-RT absolute CAC score by the time interval between two CT scans (in years). Since CT dose planning was introduced from August 2006 onwards in our institution, dosimetric data were available in 114 patients only. The contouring of each coronary artery was cooperated by two experienced cardiovascular radiologist and radiation oncologist. For left-sided BC, the mean dose and maximal dose of LAD were 1923.60 ± 906.65 cGy and 5155.59 ± 365.49 cGy (mean ± SD), respectively. The radiation doses of LAD and LCX were significantly higher in left-sided BC than those of right-sided BC (p <0.0001). However, there was no correlation between annual CACinc values and coronary radiation doses. The annual CACinc values of LAD, LCX and RCA were not significantly different in left-sided versus right-sided BC. Adjuvant chemotherapy with anthracycline- or taxane-containing regimens showed a trend of significant association with annual CACinc of LAD (p = 0.07). BC patients carrying two or more risk factors of CAD had higher annual CACinc values of LAD (p = 0.04). Our results do not support radiation-induced accelerated coronary calcium burden in BC patients treated with adjuvant RT. For BC patients undergoing adjuvant chemotherapy or carrying two or more risk factors of CAD, intensive follow of CAC increment by CT imaging may be important for early prediction of future CAD episode.