How dose sparing of cardiac structures correlates with in‐field heart volume and sternal displacement

Cardiac irradiation increases the risk of coronary artery disease in patients with left‐sided breast cancer. Techniques exist to reduce cardiac irradiation, but the optimum technique depends on individual patient anatomy and physiology. We investigated the correlation of delta heart volume in field (dHVIF) and sternal excursion with dose sparing in heart and left anterior descending artery (LAD) to develop quantitative predictive models for expected dose to heart and LAD. A treatment planning study was performed on 97 left‐breast cancer patients who underwent whole breast radiotherapy [Formula: see text] under deep inspiratory breath hold (DIBH). Two CT datasets, free breathing (FB) and DIBH, were utilized for treatment planning and for determination of the internal anatomy‐based DIBH amplitude. The mean heart and LAD dose were compared between FB and DIBH plans and dose to the heart and LAD as a function of dHVIF and sternal excursion were determined. The [Average (STD); Range] mean heart doses from free breathing and DIBH are [Formula: see text] and [Formula: see text] , respectively. The mean LAD doses from free breathing and DIBH are [Formula: see text] and [Formula: see text] , respectively. The mean dose reductions with DIBH are [Formula: see text] for the heart and [Formula: see text] for LAD. Percent mean dose reductions to the heart and LAD with DIBH are 44% [Formula: see text] and 67% [Formula: see text] , respectively, compared to FB. The dHVIF mean dose reduction correlation is [Formula: see text] for the heart and [Formula: see text] for LAD (with linear trend and y intercept: 26.0 cGy for the heart, 109.1 cGy for LAD). DIBH amplitude using sternal position was [Formula: see text]. The DIBH amplitude mean dose reduction correlation is [Formula: see text] for the heart and [Formula: see text] for LAD (with linear trend with y intercept: 35.6 cGy for the heart, 102.4 cGy for LAD). The strong correlation of dose sparing to the heart and LAD with dHVIF and sternal excursion suggests that mean dose sparing to heart and LAD can be predicted with either dHVIF or sternal excursion equally well. The metrics proposed could be utilized to allow providers to determine the relative dosimetric benefits of different heart‐sparing techniques as early as time of consultation. PACS number(s): 87.53.Tf