Abstract: Objective To observe the volumes of original foci, lymph nodes and parotid gland in nasopharyngeal carcinoma (NPC)patients during helical tomotherapy (HT). Methods Clinical data about 77 NPC patients admitted to our hospital from March 2008 to March 2012 were retrospectively analyzed.At the 20 times when the patients underwent HT at the dose of 70Gy in 33 fractions(70Gy/33F), their NPC was located one more by CT scanning.The volumes of NPC original foci, retropharyngeal lymph nodes(GTV_nx), cervical lymph nodes (GTV_nd), and parotid glands were compared. Results The volumes of GTV_nx and GTV_nd decreased 32.6%±20.7% and 47.3%±21.9%, respectively.The volumes of left and right parotid glands decreased 32.6%±20.7% and 47.3%±21.9%, respectively.The decreased volumes were positively related with the initial volumes.The volume of GTV_nx in different T stages was significantly different between the first and second CT locations (P< 0.001).The volume of GTV_nx in stages T₁-T₄ decreased (5.6±4.7) cm³, (12.6±12.3) cm³, (23.2±12.6) cm³ and (23.3±20.0) cm³, respectively (χ²=15.31, P< 0.005). Conclusion The volumes of NPC original foci, cervical lymph nodes, and parotid gland are significantly smaller after HT.The volume of NPC original foci is significantly smaller in T₃/T₄ stage than in T₁/T₂ stage.The tumor should be located once more by CT scanning and its treatment plan should be adjusted.