The benefit of deep inspiration breath hold: evaluating cardiac radiation exposure in patients after mastectomy and after breast-conserving surgery

This study aims to evaluate the reduction of cardiac radiation dose and volume with deep inspiration breath hold (DIBH) technique compared to free breathing (FB) in patients with left-sided breast cancer. The study also aims to evaluate whether the benefits of DIBH vary in patients who had whole breast radiotherapy (RT) after breast-conserving surgery (BCS) and those who had chest wall RT post-mastectomy (M). FB and DIBH plans were generated for 15 consecutive post-BCS patients and 17 post-M patients who underwent RT with DIBH using varian real-time position management (RPM) system. Cardiac shields were used in all post-BCS plans, provided that clinical treatment volume coverage was not compromised, while chest wall coverage took priority in post-M plans. The prescribed dose was 50 Gy in 25 fractions for the whole breast or the chest wall. Parameters of interest were cardiac V5, mean LAD dose, maximum LAD dose, and mean heart dose. The impact of DIBH was compared in post-BCS and post-M patients using paired t tests. To gauge clinically meaningful outcome, the proportion of patients with V5 < 5 % and mean cardiac dose < 2 Gy were compared using McNemar's test. DIBH decreased V5 by an absolute 4.5 % (2.3 vs. 6.8 %; p < 0.0001) in post-M group, and by an absolute 2.4 % (1.3 vs. 3.7 %; p = 0.0028) in post-BCS group. DIBH decreased the mean heart dose by 107.0 cGy (127.4 vs. 234.4 cGy; p = 0.0002) in post-M group, and by 58.9 cGy (82.2 vs. 141.1 cGy; p = 0.0012) in post-BCS group. DIBH decreased mean LAD by 1201.6 cGy (670 vs. 1872.5 cGy; p = 0.0006) in post-M group, and by 799.0 cGy (425.3 vs. 1224.3 cGy; p = 0.0003) in post-BCS group. DIBH also decreased max LAD dose by 1244.3 cGy (2776.0 vs. 4020.3 cGy; p = 0.0014) in post-M group, and by 1856.3 cGy (1898.7 vs. 3754.9 cGy; p = 0.0005) in post-BCS group. In post-BCS group, cardiac V5 < 5 % was achieved in 10/15 (67 %) FB patients, and in 15/15 (100 %) DIBH patients (p = 0.002), and mean heart dose < 2 Gy was achieved in 12/15 (80 %) FB patients and in 15/15 (100 %) DIBH patients (p < 0.001). This compares with post-M group, in which V5 < 5 % was achieved in 6/17 (35 %) FB patients and in 16/17 (94 %) DIBH patients (p = 0.05), and mean heart dose < 2 Gy was achieved in 7/17 FB (41 %) an 16/17 DIBH patients (94 %) (p = 0.03). The results of this study suggest that there is considerable reduction in cardiac exposure in most patients with DIBH compared to FB, although less reduction is observed in the post-BCS patients. The use of cardiac shields and collimators/gantry adjustments, more readily applicable for post-BCS cases, may limit the additional benefits of DIBH. In an environment where DIBH availability is limited, the result of this study supports the preferential use of DIBH in post-M patients over post-BCS patients.