Tangential volumetric modulated arc therapy reduces cardiac and contralateral low-dose exposure compared with continuous volumetric modulated arc therapy in postoperative breast radiotherapy

Background and purpose Tangential volumetric modulated arc therapy may combine rotational conformality with tangential beam geometry. We compared tangential with continuous-arc volumetric modulated arc therapy for postoperative breast radiotherapy with deliberately matched target coverage, focusing on cardiac and contralateral low-dose exposure. Material and methods Fifty-four patients were included in this paired planning study. For each patient, the clinically delivered tangential plan and a matched continuous-arc plan were evaluated. Target coverage was matched by clinical-target-volume D95% and planning-target-volume D2%. Dose-volume endpoints, low-dose area-under-the-curve metrics, delta dose-volume histograms, subgroup interactions, and mechanistic organ-equivalent-dose surrogates were evaluated. Results Target coverage and homogeneity were comparable, while conformity was higher with tangential planning ( p = 0.006). Tangential planning reduced mean heart dose from 1.34 to 1.17 Gy ( p < 0.001), contralateral lung mean dose from 0.94 to 0.57 Gy, and contralateral breast mean dose from 1.16 to 0.76 Gy (both p < 0.001). Mechanistic organ-equivalent-dose surrogates were reduced by 37.0% for the contralateral lung and 32.7% for the contralateral breast. Exploratory interaction analyses did not identify statistically significant interactions by laterality, deep-inspiration breath hold, simultaneous integrated boost, or regional nodal irradiation. Conclusions In a clinically heterogeneous paired cohort that included boost irradiation, regional nodal irradiation, and deep-inspiration breath hold, tangential volumetric modulated arc therapy reduced cardiac and contralateral low-dose exposure while preserving target coverage.