Is Radiation-Induced Cardiac Toxicity Reversible? Prospective Evaluation of Patients With Breast Cancer Enrolled in a Phase 3 Randomized Controlled Trial.

<bold>Purpose: </bold>Myocardial perfusion defects after breast radiation therapy (RT) correlate with volume of irradiated left ventricle (LV). We aimed to determine the relationship between myocardial perfusion, LV dosimetry, and grade ≥2 late cardiac events in patients with breast cancer undergoing adjuvant RT.<bold>Methods and Materials: </bold>A randomized study evaluated the benefit of inverse-planned intensity modulated radiation therapy over forward-planned intensity modulated radiation therapy for radiation toxicity in breast cancer. A secondary endpoint was evaluating cardiac perfusion by single-photon emission computed tomography done at baseline, 6 months, 1 year, 2 years, and 5 years post-RT. We used receiver operating curve and regression analysis to identify association between perfusion, radiation dose-volumes, and the risk of late cardiac events.<bold>Results: </bold>Of 181 patients who received adjuvant RT, 102 were patients with cancer in the left breast (called in this study the left-sided group) and 79 were patients with cancer in the right breast (called in this study the right-sided group). Median follow-up was 127 months (range, 19-160 months). A significant worsening of perfusion defects occurred after RT in the left-sided group, which improved by 1 year. Late cardiac events were found among 16 patients (17.2%) in the left-sided group and 4 patients (5.5%) in the right-sided group. Perfusion changes did not correlate with late cardiac events, but LV dose-volumes correlated with late cardiac events. Maintaining the LV volume receiving 5 Gy and 10 Gy to <42 cc and <38cc, respectively, can reduce the risk of radiation-related late cardiac events at 10 years to <5% over baseline.<bold>Conclusions: </bold>RT was associated with short-term perfusion defects that improved within 1 year and was not correlated with late cardiac events. The ventricular volumes receiving 5 Gy and 10 Gy were correlated with late cardiac events. [ABSTRACT FROM AUTHOR]