Dosimetric comparison of simultaneous integrated boost with intensity-modulated radiotherapy, volumetric modulated arc therapy, and hybrid intensity-modulated radiotherapy in patients with multiple brain metastases

Objective To evaluate the impact of simultaneous integrated boost (SIB) with different radiotherapy plans on the dosimetry of the target volume and organs at risk (OAR) in patients with multiple brain metastases (MBM), and to provide a basis for the selection of an optimal clinical radiotherapy. Methods Ten patients with MBM who were treated with whole-brain SIB radiotherapy were randomly selected in this analysis. The local imaging data from the enrolled patients were re-planned with dynamic intensity-modulated radiotherapy (dynamic IMRT), dual-arc volumetric modulated arc therapy (dual-arc VMAT), and hybrid-IMRT (h-IMRT). h-IMRT plan was created by inversely optimizing 3 and 4 fixed fields of IMRT based on conformal radiotherapy. Two-tailed Wilcoxon matched pairs signed rank sum test was performed to analyze the differences between the three radiotherapy plans in the conformity index (CI) and homogeneity index (HI) of the planning target volumes (PTV), Dmean and Dmax of OAR, monitor units (MU), and delivery time. Results CI of PTVs with VMAT plan was better than that with IMRT and h-IMRT plans (P=0.04, 0.00), and no significant difference in HI was observed between the three plans (P>0.05). There were no significant differences in CI and HI between 3 and 4 fields in dynamic IMRT (P>0.05). h-IMRT 3-and 4-field plans had significantly reduced doses to the eye lens and eyeballs than dynamic IMRT and VMAT plans (all P=0.00), and the three plans had similar doses to the brainstem and optic nerve (P>0.05). As for the MHs and delivery time, dynamic IMRT and VMAT plans showed the highest and lowest value, respectively (all P=0.00). Conclusions All the three plans meet the clinical requirements. VMAT shows the highest treatment efficiency. H-IMRT protects the eye lens and eyeballs more effectively while maintaining the doses to the PTV, with reduced MU compared with IMRT. These offer a reference for designing the radiotherapy plan in MBM patients. Key words: Brain metastases; Volumetric modulated arc therapy; Hybrid intensity-modulated radiotherapy; Dosimetry