Purpose:To quantify the advantages in prescription dose escalation from helical tomotherapy(HT)compared to LINAC-based IMRT on nasopharynx cancer.Material and methods:20 patients with nasopharynx cancer were enrolled.For each patient,a fix beam IMRT(FB-IMRT)plan was first optimized on Varian Eclipse planning system with a gradually escalated prescription dose.This process was interrupted when any of the organ at risk(OAR)achieved the dosevolume limit according to the QUANTEC criteria.Then,the same strategy was repeated on tomotherapy planning system for each patients helical tomotherapy IMRT(HT-IMRT)plan.The advantages were evaluated by comparing the final prescription dose,conformal index(CI)and homogeneity index(HI)for targets,and dose-volume histograms for OARs.Results:The dose distribution of both FB-IMRT and HT-IMRT plans for all the patients achieved the requirement of ICRU83# report.16(80%)FB-IMRT plans were interrupted for the parotids dose limitation,2(10%)for spinal-cord and 2(10%)for lens.However,no HT-IMRT plan was interrupted for the parotids dose limitation,but 8(40%)for optic-nerves,8(40%)for brain-stem and 4(20%)for spinal-cord.The final prescription dose was 57.8±5.1Gy for FB-IMRT and 81.9±10.7Gy for HT-IMRT respectively(p<0.01).The average CI and HI were 0.78±0.16 vs.0.63±0.20(p=0.86)and 0.10±0.02 vs.0.07±0.03(p=0.048)compared between FB-IMRT and HT-IMRT.Conclusions:Helical tomotherapy provides a huge potential ability of dose escalation compared to fix beam IMRT in the treatment of nasopharynx cancer.This advantage from HT-IMRT is much more significant at spring parotids while taking the cost of slight lower conformal index than FB-IMRT.