| Objectives①To study dosimetric characteristics of helical tomotherapy by compareing its treatment plans with that of linear accelerator-based step-and-shoot IMRT for NPC.②To measure set-up errors of helical tomotherapy for NPC by IGRT system,and calculate the enlargement of CTV.③To evaluate the acute side effects of helical tomotherapy for NPC from Nov.2007 to Jan.2008 in our hospital.④Review helical tomotherapy publications for head and neck carcinomas.Methods①Targets on CT images of 10 NPC patients are drawn out,and transferred to Helical Tomotherapy and IMRT treatment plan system,respectively. The prescription dose for pGTV or GTVnd,PTV1 and PTV2 was 70Gy,60Gy and 54Gy by 33 fractions.The limit doses of organs at risk:parotid V35＜50%, brain-stem＜54Gy,spinal cord＜45Gy,lens＜9Gy,etc.Data were analysed with paired t-test.②From Nov.2007 to Jan.2008,11 NPC patients treated with helical tomotherapy took total 263 image guidances.Systemic errors,random errors and Mptv were calculated and analysed,③Acute side effects of skin,parotid glands, pharynx-esophagus-trachea,oral mucosa,inner ear,larynx,and peripheral blood were studied for each patient.Results①The dose distribution is good in both groups.However the homogeneity index(HI)and Dmean of PTV1 in Tomo group are better than IMRT group(P＜0.01).The Dmean of PTV1 in Tomo group(63.84Gy)is lower than IMRT group(70.30Gy).The Dmean of parotid glands in Tomo group is 5.3Gy lower than IMRT group,with lower V35 and V30.The Dmax of larynx-esophagus is lower than/MRT group.②89.35%,89.73%and 96.96%set-up errors at X,Y and Z direction are within the range of -3.00mm and +3.00mm Both the standard deviation of systemic error and random error are≤1.50mm By different methods, MPTVis in the range of 1.93～4.77mm③No grade 3 and 4 acute side effects were noted.Conclusions①Helical tomotherapy has a better homogeneity,steeper dose gradient and better protection for organs at risk in NPC irradiation.②Mptv calculation provides the base for CTV expanding for NPC IMRT.③No severe acute effects were noted in helical tomotherapy for NPC,but more cases are needed for observation.
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