Purpose: The purpose of this study was to compare the dosimetric characteristics for protection of the hippocampus between dual arc VMAT (volumetric modulated arc therapy) and 7 fields intensity-modulated radiation therapy (7F-IMRT) for patients with brain metastases from lung cancer under the whole brain radiotherapy.
Methods: Based on ten cases with brain metastases from lung cancer, two types of radiotherapy plans were designed, namely, dual arc VMAT and 7F-IMRT. Provided that the clinical requirements were satisfied, the comparisons of target dose distribution, conformity index (CI), homogeneity index (HI), dose of organs at risk (OARs), monitor units (MU) and treatment time between dual arc VMAT and 7F-IMRT were investigated for their dosimetric difference.
Results: Both treatment plans met the requirements of clinical treatments. However, the PTV-HA conformity and homogeneity of dual arc VMAT were superior to those of 7F-IMRT (P < 0.05). As to OARs, the mean maximum doses (Dmax) of hippocampus, eyes and optic nerves in the dual arc VMAT plan were all lower than those in 7F-IMRT plan (P < 0.05), but the result had no statistical significance (P < 0.05) for the maximum dose of lens. Compared with 7F-IMRT, dual arc VMAT reduced the average number of MU by 67% and the average treatment time by 74%. Therefore, treatment time was shortened by dual arc VMAT.
Conclusion: With regards to the patients with brain metastases from lung cancer under the whole brain radiotherapy, the PTV-HA conformity and homogeneity of dual arc VMAT were superior to those of 7F-IMRT under the precise of meeting the clinical requirements. In addition, dual arc VMAT remarkably reduced the irradiation dose to OARs (hippocampus, eyes and optic nerves), MU and treatment time, as well, guaranteed patients with better protection.
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