Evaluation of Dose to Heart and Left Anterior Descending Coronary Artery during Left Breast Irradiation

Abstract

Purpose: The aim of this retrospective study is to quantify dose irradiated to the heart and the left anterior descending coronary artery (LADCA) in left breast cancer patients treated with adjuvant breast radiotherapy and analyse the probable causes of high dose to the heart and LADCA. Methods and Materials: Twenty-one consecutive patients with left-sided breast cancer who underwent adjuvant radiotherapy to the breast between August 2012 and October 2013 are enrolled in our study. All patients were irradiated with 6- or 10-MV tangential beams to the breast and seven patients of them also received supraclavicular fossa (SCF) irradiation with IMRT technique. For each dose plan, dose-volume histograms (DVHs) for the heart and LADCA were calculated and analyzed. Pearson correlation coefficient was calculated to assess the relationship between average heart D_(mean) (mean dose), LAD D_(mean) and LAD_(max) (maximum dose) and between LAD D_(mean) and volume of LADCA in the radiation fields (i.e., it received ＞25 Gy). Student's t test was used to assess the statistical significance of differences in radiation dose to LADCA and heart between patients who received SCF IMRT or not. Results: For the 21 patients given left breast irradiation, the average mean [range] dose was 4.04 [1.75-11.15] Gy to the heart and 21.29 [6.99-35.28] Gy to the LADCA, and the average maximum dose was 54.31 [50.55-58.42] Gy to the LADCA. There is significant correlation between D_(mean) to the heart and LADCA (r= 0.80, p ＜ 0.01). The D_(mean) to LADCA was postulated to increase 3.44 Gy for each increase of 1 Gy in the mean radiation dose delivered to the heart in our study. There is significant correlation between Dmean to LADCA and the volume of LAD in the radiation fields (i.e., it received ＞25 Gy) (r= 0.94, p＜ 0.0001). The D_(mean) to LADCA was postulated to increase 0.77 Gy for each increase of 1 ml of LADCA volume in the radiation field. For 7 patients who received left-tangential radiotherapy and SCF IMRT, the average mean dose was 4.15 [2.58-8.9] Gy to the heart and 21.93 [16.49-35.21] Gy to the LADCA, and the average maximum dose was 55.21 [52.63-57.79] Gy to the LADCA. SCF IMRT contributed to average mean dose 0.15 [0.05-0.35] Gy and average maximum dose 0.43 [0.15-0.68] Gy to the LADCA. There is no significant difference in Dmean to the LADCA and heart between patients who received SCF IMRT or not (p= 0.38, p= 0.45, respectively). Conclusion: For patients receiving left-tangential radiotherapy, the higher Dmean to the LADCA was strongly correlated to the larger volume of LADCA in the radiation fields. There is significant correlation between D_(mean) to the heart and LADCA. The patients with the higher mean heart dose had the higher mean LADCA dose. We may suggest to limit mean dose to LADCA by avoiding volume of LADCA in the treatment fields if well visualized LADCA on CT scan or limiting the mean heart dose to lower mean LADCA dose if poor visualization of LADCA on CT scan.