Use of maximum heart distance to evaluate heart dosimetry for tangential field radiotherapy in left-sided breast cancer after modified radical mastectomy

Objective To assess the value of maximum heart distance (MHD) in predicting the dose of tangential field heart irradiation in left-sided breast cancer. Methods A total of 40 left-sided breast cancer patients who were given adjuvant tangential field irradiation on the left chest wall after modified radical mastectomy in our hospital from January 2010 to December 2011 were selected in this study. For each patient, the following parameters were derived using three-dimensional treatment planning system: MHD, mean dose (Dmean) to organs at risk including the whole heart, left anterior descending (LAD) coronary artery, left ventricle (LV) , and anterior myocardial territory (AMT) , thickness of the contralateral breast tissue, and thickness from the sternum to the body surface (measuring body fat). The relationship between MHD and each Dmean was analyzed by curve fitting equation. The reliability of R2> 0.8 represented a good correlation. Results The MHD of 40 patients was between 1.14 and 5.34 cm ((2.66±0.16) cm)). The R2 values of first-, second-, and third-order curve fitting equations were 0.869, 0.875, and 0.883, respectively, between MHD and whole heart Dmean (all P=0.000) ; 0.777, 0.799, and 0.813, respectively, between MDH and AMT Dmean (all P=0.000) ; 0.598, 0.601, and 0.633, respectively, between MHD and LV Dmean (all P=0.000) ;and 0.418, 0.470, and 0.472, respectively, between MHD and Dmean of the LAD coronary artery (all P=0.000). The Dmean of all the heart compartments was not affected by the body fat thickness. Conclusions MHD is a reliable predictor of the mean dose to organs at risk (whole heart and AMT) in tangential field radiotherapy for left-sided breast cancer. Key words: Maximum heart distance; Mean heart dose; Breast neoplasm/radiotherapy