The Prediction of Radiation-Induced Trismus by the Apparent Diffusion Coefficient Values of Masseter Muscles before Chemoradiotherapy in Locally Advanced Nasopharyngeal Carcinomas.

Purpose: Although the apparent diffusion coefficient (ADC) value from diffusion-weighted imaging can provide insights into various pathological processes, no studies have examined the relationship between the pre-concurrent chemoradiotherapy (CCRT) mean ADC (ADC) values of the masseter muscles and radiation-induced trismus (RIT) in locally advanced nasopharyngeal carcinoma (LA-NPC) patients. Therefore, the current research aimed to investigate the significance of pre-CCRT masseter muscle ADC values for predicting the RIT rates in LA-NPC patients treated with definitive CCRT.

Materials And Methods: The pre-CCRT ADC values of the masseter muscles and the post-CCRT RIT rates were evaluated. A receiver operating characteristic curve analysis was employed to determine the optimal ADC cutoff. The primary objective was to examine the relationship between the pre-CCRT masseter muscle ADC values and the post-CCRT RIT rates.

Results: Seventy-seven patients were included. The optimal ADC cutoff value was 1381.30 × 10 mm/s, which divided the patients into two groups: an ADC < 1381.30 × 10 mm/s (n = 49) versus an ADC > 1381.30 × 10 mm/s (n = 28). A masseter muscle ADC > 1381.30 × 10 mm/s was found to be associated with significantly higher RIT rates than an ADC < 1381.30 × 10 mm/s (71.42% vs. 6.12%; < 0.001). The multivariate analysis results confirmed a pre-CCRT masseter muscle ADC > 1381.30 × 10 mm/s as an independent predictor of RIT.

Conclusions: Our study presents the first evidence establishing a connection between elevated masseter muscle ADC values and higher RIT rates in LA-NPC patients following CCRT. If confirmed with further research, these findings may help to categorize the risk of RIT in these patients.