Intensity-modulated radiotherapy for nasopharyngeal carcinoma: the reduction of radiation-induced trismus.

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.