Abstract
Objective To compare the dose distribution between volumetric-modulated arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) in patients with brain metastases receiving hippocampus-sparing whole brain radiotherapy. Methods Forty-six patients with brain metastases admitted to our hospital from 2013 to 2016 were recruited in this study. After fusing the CT and MRI images, the hippocampus was delineated on the fusion images. The three-grade hippocampal avoidance regions were created by using a volumetric expansion of 3, 5 and 10 mm surrounding the hippocampus. The planning target volume (PTV) was calculated by subtracting the 5-mm expansion surrounding the hippocampus from the whole brain. The prescription dose was 30 Gy/10 fractions. The 7-field IMRT and single arc VMAT were designed for each case. The dose distribution of PTV, hippocampus and other organs at risk (OARs) were evaluated in both plans. Results The PTV was statistically compared between VMAT and IMRT: V95: 95.90% and 94.97%(P=0.000); V90: 98.17% and 97.48%(P=0.000); CI: 0.825 and 0.813(P=0.013); HI: 0.277 and 0.289(P=0.025). The hippocampal dose was also compared between VMAT and IMRT: the Dmax of hippocampus was 1 698.9 cGy for VMAT and 1 784.9 cGy for IMRT (P=0.002). The Dmean of hippocampus was 1 183.8 cGy for VMAT and 1 112.7 cGy for IMRT (P=0.000). No statistical significance was observed between IMRT and VMAT in protecting the OARs except the chiasma opticum (3 262.6 cGy and 3 529.3 cGy, P=0.000). The MU and treatment time of VMAT and IMRT were 651 and 2 768(P=0.000), and 188 s and 504 s (P=0.000). Conclusions The dose distribution of PTV in VMAT is significantly better than that in IMRT.VMAT is advantageous in protecting the hippocampus than IMRT.VMAT can significantly shorten treatment time and MU and enhance the equipment utilization. Besides, VMAT can achieve the goal of protecting the hippocampus and meet the prescription dose requirement of PTV. Key words: Neoplasms metastasis, brain/whole brain radiotherapy; Hippocampus-sparing; Neoplasms metastasis, brain/radiotherapy
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