| Objective:Aims at a dosimetric comparison of radiation therapy planning for single arc VMAT(S-VMAT), double arc VMAT(D-VMAT) and five beam ports IMRT of the esophageal cancer(EC), respectively.Methods:seventeen patients were selected,including ten located in the cervical and seven located in the lower thoracic EC. Three plans were generated with Pinnacle V9.2 of Philips Company for each patient. The prescribed doses were 63Gy/30F/6W for GTV-PTV and 54Gy/30F/6W for CTV-PTV. The planning target volume coverage and protections on organs at risk(OARs) of three plans were compared. The monitoring units(MU) and the delivery time for different plans were compared.Results:(1) For the cervical EC, Plans of IMRT, S-VMAT and D-VMAT showed significant statistic difference in D95, D98, D50, D2, HI and CI of GTV-PTV and CTV-PTV. The sequence of HI and CI, from the best to the worst, is D-VMAT, S-VMAT, IMRT. There were significantly different in D max and V2 of the spinal cord in the three plans. The sequence of D max and V2, from the highest to the lowest, is IMRT, S-VMAT, D-VMAT. The V31.5 of E-P in all of VMAT was lower than those in the IMRT, at the expense of increasing V5 and V10. Compared to IMRT, VMAT decreased MU by 30.5% with S-VMAT and 14.1% with D-VMAT, respectively.(2) For the lower thoracic EC, IMRT, S-VMAT and D-VMAT generated similar dose distributions for GTV-PTV, CTV-PTV and OARs. However, compared to IMRT, the MU was decreased by 23.9% with S-VMAT and 14.5% with D-VMAT.(3) The delivery time of IMRT, S-VMAT and D-VMAT was 7?10min, 1?2min and 3?4min, respectively. Comparison of plans, VMAT resulted in significant reductions in delivery time.Conclusion:Compared to IMRT, the main advantage of VMAT is a decreased MU and shortend delivery time. For the cervical EC, VMAT was superior to IMRT,the CI and HI of PTV and the OARs in plan of D-VMAT was better than in plan of S-WMAT. For lower thoracic EC, there weren’t significant among three plans. |
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