Purpose:To evaluate the impact of complexity indices on the plan quality and deliverability of the volumetric modulated arc therapy(VMAT),and to determine the most significant parameter in the development of an ideal clinical VMAT plan.Methods:A multi-dimensional exploratory statistical method-canonical correlation analysis was adopted to study the correlations,as well as the contribution weights,of treatment plan parameters of complexity,quality and deliverability for 32 nasopharyngeal cancer with two-arc VMAT plans and 31 esophageal cancer patients with one-arc VMAT plans.Results:The average PTV volumes of NPC and esophageal cancer patients were 826.4±203.9,and 662.4±271.8 cm 3,respectively.The average total MU of two-arc NPC patients were 672.3±54.4 versus 538.1±87.5 of one-arc esophageal caner patients.MU per arc(MU/ARC)and MU per control point(MU/CP)of NPC were 337.8±25.2 and 3.7±0.3,respectively,which were significantly lower than those of esophageal cancer patients(MU/ARC :475.0±100.0,MU/CP :5.2±1.1); The proportion of MU/CP less than 3 was higher and the proportion of SA less than 50 cm 2 was lower in the NPC groups compared with esophgeal cancer patients.The average segment area of control points(SA/CP)of NPC patients were larger than(p=0.013)those of esopageal cancer(66.3±9.4 vs.58.1±15.4 cm 2).MCSv per arc of NPC was lower than that of esophageal cancer patients.All these plan complexity indices indicated that two-arc VMAT plans of NPC were more complex than one-arc VMAT plans of esophageal cancer patients.Canonical correlation analysis indicated that plan complexity parameters were highly correlated with plan quality,but not with deliverability,in which MU/CP and MU/ARC were contribute the greatest weights.Conclusions:We have quantified various plan characteristics in terms of complexity,quality,and deliverability.MU/CP and MU/ARC were found to have strong effect on the plan quality,but not on deliverability.New robust deliverability parameters instead of relative gamma passing rate should be investigate for further study.