Cardiotoxic Effects of Tangential Breast Irradiation in Early Breast Cancer Patients: The Role of Irradiated Heart Volume
Purpose: To assess the risk of cardiovascular disease (CVD) after postlumpectomy irradiation restricted to tangential fields. Methods and Materials: We assessed the incidence of CVD in 1601 patients with T1-2N0 breast cancer (BC) treated with breast tangentials in five different hospitals between 1980 and 1993. Patients treated with radiation fields other than breast tangentials and those treated with adjuvant chemotherapy were excluded. For patients with left-sided BC, maximum heart distance (MHD) was measured on the simulator films as a proxy for irradiated heart volume. Risk of CVD by laterality and MHD categories was evaluated by Cox proportional hazards regression analysis. Results: Follow-up was complete for 94% of the patients, and median follow-up was 16 years. The incidence of CVD overall was 14.1%, of ischemic heart disease 7.3%, and for other types of heart disease 9.2%, with a median time to event of 10 to 11 years. The incidence of CVD was 11.6% in patients with right-sided BC, compared with 16.0% in left-sided cases. The hazard ratio associated with left-sided vs. right-sided BC was 1.38 (95% confidence interval [CI], 1.05-1.81) for CVD overall, 1.35 (95% CI, 0.93-1.98) for ischemic heart disease, and 1.53 (95% CI, 1.09-2.15) for other heart disease, adjusted for age, diabetes, and history of CVD. The risk of CVD did not significantly increase with increasing MHD. Conclusions: Patients irradiated for left-sided BC with tangential fields have a higher incidence of CVD compared with those with right-sided cancer. However, the risk does not seem to increase with larger irradiated heart volumes.