中文摘要：

目的探讨应用螺旋断层放疗（HT）进行鼻咽癌放疗处方剂量提升的可行性及剂量学特点。方法选取10例9野静态调强放疗的鼻咽癌计划，制定HT计划和静态调强（sIMRT）计划。在危及器官（OAR）符合正常组织临床影响量化分析标准的前提下，提升两组计划处方剂量，并比较剂量提升空间及处方剂量提升后两者的剂量学差异。结果与sIMRT计划相比，HT计划所达到的处方剂量比sIMRT计划增加了42．6％（t=6．373．P〈0．01）；处方剂量提升后，HT计划的均匀性指数仍优于sIMRT计划（t=-2．288，P〈0．05），但适形度指数略低于sIMRT计划（P〉0．05）。限制HT计划处方剂量提升的OAR为脊髓（2例）、视神经（5例）、脑干（3例）；限制sIMRT计划处方剂量提升的OAR为眼晶状体（1例）、脊髓（1例）、腮腺（8例）。结论HT的高束流调强能力，使其在有效保护OAR的前提下．能够提高鼻咽癌放疗处方剂量。在sIMRT实现高处方剂量要求存在困难时．可考虑使用HT进行放疗。

英文摘要：

Objective To study the feasibility of helical tomoterapy （HT） at prescription dose escalation for nasopharyngeal carcinoma （ NPC ）. Methods Static-IMRT （sIMRT） and HT plans were designed for 10 nasopharyngeal carcinoma patients which were treated by sIMRT and HT treatment plan. Prescription dose was escalated for each plan until any organs at risk （ OARs ） reached the quantitative analysis of normal tissue effects within the clinical threshold. Dosimetric factors of target and OARs were analyzed for both sIMRT and HT plans. Results Compared with sIMRT plan, prescribed dose of HT plans increased 42.6% （ t = 6. 373, P 〈 0.01 ） , and the homogeneity＂ index was also improved （ t = - 2. 288, P 〈 0. 05） ; the conformity index decreased （ P 〉 0. 05 ）. The limits of HT prescribed dose escalation were spinal cord （2 cases） , optic nerve （5 cases） and hrainstem （3 cases）. The limits of sIMRT prescribed dose escalation were lens （1 case）, spinal cord （l case） and parotid （8 cases）. Conclusions HT could improve prescription dose of nasopharyngeal carcinoma while keeping the OARs safe. Compared with slMRT, HT technology might be used at high dose NPC radiotherapy.