Background: While DIBH is routinely utilized for left-sided breast cancers, its benefits for rBC have yet to be established. We compared free-breathing (FB) and DIBH treatment plans for a cohort of rBC undergoing RNI to determine its potential benefits. Methods: rBC patients considered for RNI (IMNs, supraclavicular field, +/- axilla) from 10/2017-5/2020 were included in this analysis. For each patient, FB vs. DIBH plans were generated and dose volume histograms evaluated the following parameters: mean lung dose, ipsilateral lung V 20 /V 5 (volumes of lung receiving 20 Gy and 5 Gy, respectively); mean heart dose and heart V 5 (volumes of heart receiving 5 Gy); liver V 20 absolute /V 30 absolute (absolute volume of liver receiving 20 Gy and 30 Gy, respectively), liver D max, and total liver volume irradiated (TVI liver ). The dosimetric parameters were compared using Wilcoxon signed-rank testing. Results: 54 patients were eligible for analysis, comparing 108 FB and DIBH plans. DIBH significantly decreased all lung and liver parameters: mean lung dose (19.7Gy to 16.2Gy, p<0.001), lung V 20 (40.7% to 31.7%, (p<0.001), lung V 5 (61.2% to 54.5%, p<0.001), TV liver (1446cc vs 1264cc; p=0.006) liver D max (50.2 Gy vs 48.9 Gy; p=0.023), liver V 20 (78.8cc to 23.9cc, p<0.001) and liver V 30 (58.1cc to 14.6cc, p<0.001) when compared with FB. As expected for rBC, DIBH use did not significantly improve heart parameters, although the V 5Heart trended on significance (1.25 to 0.6, p=0.067). Conclusion: This is the largest cohort to date analyzing DIBH for RNI-rBC. Our findings demonstrate significant improvement in all lung and liver parameters with DIBH, supporting its routine use for rBC pts being considered for comprehensive RNI. This study suggests that DIBH should be strongly considered in routine clinical practice for RNI-rBH to reduce lung and liver doses.
Wilcoxon signed rank test of each dosimetric endpoint