The purpose of this study was to evaluate the degree of radiation-induced trismus after intensity-modulated radiotherapy (IMRT) in patients with nasopharyngeal carcinoma (NPC). From 2003 to 2004, 17 non-metastatic NPC patients treated with parotid-sparing IMRT were enrolled. The maximal interincisal distance (MID) was measured to represent the maximum mouth opening. All 17 patients had both pre- and post-IMRT measurements taken, and the normalized MID (post-IMRT MID/pre-IMRT MID) was analysed to evaluate the percentage decrease in MID after IMRT. The median follow-up time was 20.5 months. One patient had nodal failure and was successfully salvaged with radiotherapy. All 17 patients were alive without cancer at the last follow-up. The average MID before IMRT was 46.2 mm (standard deviation (SD), 8.6 mm). The average MID at 12 months post-IMRT was 45.4 mm (SD, 8.9 mm). The averages of normalized MID were 94% (SD, 3.9%) at 5 months post-IMRT and 98.1% (SD, 4.2%) at 12 months post-IMRT. Based on the satisfactory preservation of normalized MID (average of 98.1% at 12 months post-IMRT), we demonstrate that IMRT reduces radiation-induced trismus in NPC patients. The recovery of normalized MID exists in the period from 5-12 months post-IMRT.

A better result can be obtained by starting with a DV-generated plan and then improving it by adding gEUD-based improvements to reduce the number of iterations and to improve the optimum dose distribution. Advances to knowledge The DV-gEUD plan provided superior dosimetric results for treating BBC in terms of PTV coverage and OAR sparing than the DV plan, without sacrificing the homogeneity of dose distribution in the PTV.