ABSTRACT
Objective To study dosimetric characteristics of helical tomotherapy (HT) by comparing its treatment plans with linear accelerator-based step-and-shoot intensity modulated radiation therapy (IMRT) for nasopharyngeal carcinoma(NPC). Methods Targets on CT images of 10 NPC patients were delineated and transferred to HT and IMRT treatment plan systems. The prescription dose was 70 Gy/33 f for pGTV and GTVnd,60 Gy/33 f for FTV1 ,and 54 Gy/33 f for PTV2. The limit dose of organ at risk was parotid V35 ＜50% ,brain-stem＜54 Gy,spinal cord ＜45 Gy and lens ＜9 Gy. Data of the two groups were compared by paired t-test. Results The dose distribution, conformality and homogeneity were good in both groups.But the homogeneity index(HI) and Dmean of PTV1 in HT group were better than IMRT group( P ＜ 0.01 ).The Dmean of PTV1 in HT group(63.84 Gy)was lower than IMRT group(70.30 Gy). The Dmean, V35 and V30 of parotids,and the Dmax of larynx-esophagus were lower in HT group than IMRT group. Conclusions Helical tomotherapy treatment plan has a better homogeneity, steeper dose gradient, and a better protection for organs at risk.