Dosimetric comparison of equispaced fields and non-equispaced fields in VMAT and IMRT for Nasal cavity and paranasal sinus cancer

PANJiannan; FENGHuiyi; DENGYongjin

Abstract：ObjectiveTo compare dosimetric differences between intensity modulated radiotherapy( IMRT) and volumetric modulated arc therapy (VMAT) in the radiotherapy plan of nasal cavity and paranasal sinus cancer, provide reference basis for selecting the best clinical treatment.MethodsTen patients with nasal cavity and paranasal sinus cancers were selected. The patients were received the VMAT plans which were created as non-equispaced fields of VMAT and equispaced fields of VMAT, and IMRT plans which were created as non-equispaced fields and equispaced fields of 5 beams and 7 beams. Dosimetry of different design methods were compared to assess the coverage rate, heterogeneity index (HI) and conformity index (CI) in the target volum, exposure dose of the organs at risk and therapeutic efficiency.ResultAll of coverages of IMRT plans and VMAT plans met the criteria of clinic. VMAT plans were still better than IMRT plans, the differences between IMRT plans of 5 beams were significant.For CI of PTV1, VMAT (including partial arc and full arc) were better than IMRT(including non-equispaced fields and equispaced fields) . Exposure dose of the organs at risk: for brain stem, Dmax and D1% of VMAT plans were lower than IMRT plans, and D1% of partial arc were lower than full arc (P<0.05). For Lens, VMAT plans had a same or better protective effect than IMRT plans, Dmax and D1% of VMAT plans were lower than most of those of IMRT(P<0.05). For Optic nerves-Ipsilateral, Dmax of VMAT plans were lower than those of IMRT (P<0.05). For Chiasm, Dmax and D1% of VMAT plans were lower than most of those of IMRT (P<0.05). For Parotid-Ipsilateral, Dmean of VMAT plans were lower than most of those of IMRT(P<0.05). Compared with IMRT plans, VMAT plans showed fewer MUs (about 1/3) (P<0.05).ConclusionNon-equispaced field can be considered as the radiotherapy field design of Nasal cavity and paranasal sinus cancer.Depending on the machine conditions, the partial arc of VMAT is more advantageous than the non-equispaced fields of IMRT.