Dosimetric comparison of IMRT and VMAT with deep inspiration breath hold or free breathing for right-sided whole breast irradiation

To compare dosimetric outcomes of intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT), with and without deep inspiration breath hold (DIBH), in patients with right-sided early-stage breast cancer receiving whole-breast irradiation (WBI) without nodal targets. Thirty-two patients with node-negative right breast cancer underwent computed tomography simulation in free-breathing (FB) and DIBH. Four plans per patient were generated: IMRT-FB, IMRT-DIBH, VMAT-FB, and VMAT-DIBH. All plans delivered 40 Gy in 15 fractions to the whole breast. Dosimetric comparisons of target and organ-at-risk (OAR) structures were performed using paired analyses and linear mixed-effects models. A Bonferroni-adjusted significance threshold of p < 0.001 was applied. VMAT significantly improved target coverage and dose homogeneity compared to IMRT (median PTV V95%: 99.5% vs. 93.4% under FB and 99.5% vs. 92.2% under DIBH, both p < 0.001), but resulted in greater low-dose exposure to the left breast (mean dose, V4, and D0.03 cc) and left lung (V5). VMAT also increased right lung doses (V5 and V16, and mean dose) and liver V5 under FB. DIBH significantly reduced various heart, lung, and liver dose parameters without compromising target coverage. Mean heart dose was lowest with IMRT (0.4 Gy). Liver D2cc (median 2.7 Gy IMRT-DIBH, 3.0 Gy VMAT-DIBH, both p < 0.001 vs. FB) and V5 (median 0% IMRT-DIBH, 0.1% VMAT-DIBH, both p < 0.001 vs. FB) were significantly reduced with DIBH. DIBH had limited effect on reducing right lung V5 but improved higher-dose sparing (V16, V20, and mean dose). Mixed-effects modelling confirmed that VMAT and DIBH independently affected dose metrics. The average beam-on time was longest for VMAT-DIBH (4.6 min) and shortest for IMRT-FB (3.4 min). DIBH improves OAR sparing for right-sided WBI without compromising target coverage, although absolute OAR doses remained low across all techniques. VMAT improves PTV coverage but increases low-dose exposure to normal tissues; however, these findings are specific to the institutional planning approach and delivery technology implemented. The combination of VMAT with DIBH should be individualised based on anatomy and clinical resources. These findings support the optional use of DIBH in right-sided WBI where dosimetric optimisation is prioritised.