| Objective: This study is to compare the oral cavity dosage of conventional radiotherapy and 3 different kinds of Intensity Modulated Radiotherapy for nasopharyngeal carcinoma (NPC), trying to figure out a most appropriate method of low oral cavity dose without target compromise.Material and Methods: Between Apr 2009 and Jun 2009, TPS (Treatment Planning System) data of 10 consecutive IMRT treated NPC patients was collected. The primary treatment plan was named as Applied. Under the same optimization parameter, we design two new IMRT plans ,Opposed (30°,80°,130°,180°,230°,280°,330°)and South(80°,110°,140°,180°,210°,240°,280°).A conventional radiotherapy plan was also designed in the same treatment volume (Routine group). Analysis with Univariate Analysis of Variance and paired test (LSD).Results: Comparing the conventional radiotherapy protocol to each of the other 3 IMRT groups, they all showed significantly difference in dose coverage of PTVnx (P<0.05); whereas there is no significant difference between the 3 IMRT groups in dosage in PTVnx.This happened to be the same case in CI (P<0.001).Oral cavity Min Dose and Mean Dose of the conventional radiotherapy group were significantly lower than each of the 3 IMRTs. Similar in V30, V35 and V40, conventional radiotherapy is significantly lower. From V45, V50 to V55, all of the 4 protocols had no significant difference. However, in V60, conventional radiotherapy was higher than IMRTs with statistical differernces.Conclusions: There were significant differences between conventional radiotherapy protocal and the other 3 IMRTs in dose coverage of PTVnx and oral cavity, but not among the IMRTs. The conventional radiotherapy protocol had smaller volume in low dosage(>25Gy) but larger volume in high dosage(>55Gy) compares to the 3 other IMRT protocols. The radiation induced oral mucositis may relate to local high dose irradiation rather than mean dose of the whole organ. There is no significantly difference between the 3 IMRT plan methods.
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