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Postoperative radiation therapy (RT) for left-sided breast cancer patients may be cause of heart toxicity. Deep inspiration breath hold (DIBH) technique reduces cardiac radiation exposure. The aim of this study Is to compare the dose distribution to cardiac substructures between DIBH and free breathing (FB) technique.

Cardiac substructures, cardiac chambers and coronary vessels, were delineated according to ESTRO guidelines on the simulation CT scans of ten left-sided breast cancer patients having undergone conserving surgery and breast RT. The plans were simulated in both, FB and DIBH CT scan in each patient to be equivalent for target coverage, namely 95% prescription dose (40 Gy In 15 fractions on whole breast plus 10 Gy In for fraction on tumor bed when appropriate) to 95% of target volume. Mean doses to the heart, cardiac substructures were retrieved and compared between DIBH and FB simulation plans.

DIBH technique obtained a statistically significant decrease for all cardiac substructures evaluated, except for left circumflex artery. The average mean heart dose was reduced from 1.45 to 1.03 Gy (p 0.008). The mean dose to the LAD coronary artery was reduced from 5.56 to 2.89 Gy (p 0.009); the mean dose to the left ventricle was reduced from 2.13 to 1.42 Gy (p 0.016). 

The dosimetric benefit of DIBH over FB therapy was consistently observed for all cardiac substructures. The DIBH technique promises a significant advantage in ameliorating the heart toxicity profile of left breast Irradiation.