Effects of collimator angle on volumetric modulated arc therapy plans for two brain metastases
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《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]
- Issue:
- 2018年第12期
- Page:
- 1399-1403
- Research Field:
- 医学放射物理
- Publishing date:
Info
- Title:
- Effects of collimator angle on volumetric modulated arc therapy plans for two brain metastases
- Author(s):
- ZHANG Ping1; DAI Peng1; LUO Longhui1; DENG Guanhua1; HUANG Qing1; WANG Jun2
- 1. Department of Oncology, Guangdong Sanjiu Brain Hospital, Guangzhou 510510, China; 2. Department of Nerosurgery, Nanfang Hospital, Southern Medical University, Guangzhou 510515, China
- Keywords:
- ; Keywords: volumetric modulated arc therapy; collimator angle; brain metastases; gradient index; monitor unit
- PACS:
- R815.6
- DOI:
- DOI:10.3969/j.issn.1005-202X.2018.12.006
- Abstract:
- Abstract: Objective To investigate the effects of multileaf collimator angle on the dosimetric parameters and monitor units (MU) of volumetric modulated arc therapy (VMAT) for patients with two intracranial metastases. Methods The CT images of 10 patients receiving radiotherapy for two intracranial metastases were selected in this study. When the collimator angle remained at zero degree, and the collimator was adjusted to reduce radiation dose to brain tissue in every arc (collimator angle was nonzero degree), VMAT plans were designed for various collimators without changing any optimization parameters. The conformity index, gradient index (GI), homogeneity index (HI), MU, and dose to organs-at-risk and normal tissues around target areas were calculated and analyzed. Results Target conformity index was similar in VMAT plans with collimator angle of zero degree and nonzero degree (t=1.084, P=0.32), but VMAT plans with collimator angle of nonzero degree had lower GI and HI, with statistical significance (GI: t=3.415, P=0.014; HI: t=3.455, P=0.014). Compared with VMAT plans with collimator angle of zero degree, VMAT plans with collimator angle of nonzero degree had smaller volume of normal tissues receiving 2 and 4 Gy (P=0.018, P=0.045), but similar volume of normal tissues receiving 6, 12 and 16 Gy (P>0.05). No statistical differences were found in the maximum dose to organs-at-risk between two plans. Moreover, the comparison between two plans showed that MU was reduced by 282 MU in VMAT plans with collimator angle of nonzero degree. Conclusion The optimal selection of collimator angle in VMAT plans for two brain metastases not only improves GI and dose coverage, but also reduces doses in low dose areas and MU.
Last Update: 2018-12-24