Comparison of six irradiation techniques for delivering hypofractionated whole-breast radiotherapy with a simultaneous integrated boost after breast-conserving surgery

To compare the following techniques for hypofractionated whole-breast irradiation (WBI) with simultaneous integrated boost (SIB) after breast-conserving surgery (BCS): three-dimensional conformal radiation therapy plus electron boost (3DCRT-EB), intensity-modulated radiation therapy (IMRT) plus EB (IMRT-EB), field-in-field IMRT plus EB (FIF-IMRT-EB), FIF-IMRT plus IMRT boost (FIF-IMRT-IB), IMRT plus IMRT boost (IMRT-IB), and volumetric-modulated arc therapy (VMAT) plus VMAT boost (VMAT-VB). Twenty patients with left breast cancer were enrolled. The prescribed dose was 40.05 Gy in 15 fractions to the whole breast and an SIB to the tumor bed of 3.2 Gy/fraction (total, 48 Gy). Target-volume coverage, dose-conformity index, homogeneity index (HI), doses to organs at risk (OAR), and costs were compared. FIF-IMRT-EB performed the best, while FIF-IMRT-IB, IMRT-IB, and VMAT-VB performed the worst. The mean dose to the planning target volume for breast evaluation (PTV Eval-breast) was significantly lower for IMRT-EB and FIF-IMRT-EB than for the other plans. For both PTV Eval-breast and PTV Eval-boost, VMAT-VB had the lowest target-volume coverage for 95% of the prescription dose and the highest target-volume coverage for >105% of the prescription dose. Among the six plans, VMAT-VB had the best HI for PTV Eval-boost and the highest doses to all OAR, except the coronary artery. Plans with EBs had lower mean doses for the contralateral lung and contralateral breast than plans with IMRT boosts. FIF-IMRT-EB had a low cost; plans with IMRT boosts had the highest costs. FIF-IMRT-EB may be the most suitable irradiation technique for hypofractionated WBI with SIB after BCS.