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Purpose Deep inspiration breath hold (DIBH) reduces heart and pulmonary doses during left-sided breast radiation therapy (RT); however, there is limited information whether the reduction in doses is similar in patients with modified radical MRM (MRM) and breast conservation surgery (BCS). The primary objective was to determine whether DIBH offers greater dosimetric reduction in cardiac doses in patients with MRM as compared to BCS with secondary objectives of documenting time consumed in counseling, simulation and planning such techniques. Methods Thirty patients with diagnosis of left sided breast cancer underwent CT simulation both free breathing (FB) and DIBH. Patients were grouped into two cohorts: MRM (n = 20) and BCS (n = 10). 3D-conformal plans were developed and FB was compared to DIBH for entire group (n = 30) and each cohort using Wilcoxon signed-rank tests for continuous variables and McNemar's test for discrete variables. The percent relative reduction conferred by DIBH in mean heart (Dmean heart) and left anterior descending artery dose (LADmean and LADmax), heart V25,V10, V2 and ipsilateral DmeanLung,V20, V12 were compared between the two cohorts using Wilcox rank-sum testing. A two-tailed p-value ≤ 0.05 was considered statistically significant. Time consumed during FB and DIBH from patient counseling to planning was documented. Results Patients undergoing BCS had comparable boost target coverage on DIBH and FB. For the overall group (n = 30), DIBH reduced Dmean heart and LAD dose, V25, V10 and V2 doses for the heart and Ipsilateral DmeanLung, V20, V12 which was statistically significant. For individual cohorts DIBH did not significantly reduce the lung (Ipsilateral DmeanLung, V20, V12) and LAD (LADmean and LADmax) doses for BCS while significant reduction in all cardiopulmonary doses was seen in MRM cohort. Despite significant reductions with DIBH in MRM, ipsilateral lung constraint of V12 Conclusion DIBH led to significant reduction of cardiac doses in both MRM and BCS. Reduction of lung and LAD doses were significant in MRM cohort. All cardiac constraints were met with DIBH in both cohorts, lung constraints were less frequently met in MRM cohort requiring nodal radiation.