Purpose: To investigate the feasibility of partial arc volumetric modulated arc\ntherapy (VMAT) in lung cancer stereotactic body radiotherapy (SBRT), as\nwell the volumetric and dosimetric effects of different internal target volume\n(ITV) definitions with 4D CT. Methods: Fourteen patients with primary and\nmetastatic lung cancer underwent SBRT were enrolled. Full and partial arc\nVMAT plans were generated with four different ITVs: ITVall, ITVMIP, ITVAIP\nand ITV2phases, representing ITVs generated from all 10 respiratory phases,\nmaximum intensity projection (MIP), average intensity projection (AIP), and\n2 extreme respiratory phases. Volumetric and dosimetric differences, as well\nas MU and delivery time were investigated. Results: Partial arc VMAT irradiated\nmore dose at 2 cm away from planning target volume (PTV) (P =\n0.002), however, it achieved better protection on mean lung dose , lung V5,\nspinal cord, heart and esophagus compared with full arc VMAT. The average\nMU and delivery time of partial arc VMAT were 240 and 1.6 min less than\nthose of full arc VMAT. There were no significant differences on target coverage\nand organ at risks (OARs) sparing among four ITVs. The average percent\nvolume differences of ITVMIP, ITVAIP and ITV2phases to ITVall were 8.6%,\n13.4%, and 25.2%, respectively. Conclusions: Although partial arc VMAT\ndelivered more dose 2 cm out of PTV, it decreases the dose to lung, spinal\ncord, and esophagus, as well decreased the total MU and delivery time compared\nwith full arc VMAT without sacrificing target coverage. Partial arc\nVMAT was feasible and more efficient for lung SBRT.
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