Evaluation of salivary gland function using diffusion-weighted magnetic resonance imaging for follow-up of radiation-induced xerostomia

To investigate the value of diffusion-weighted magnetic resonance imaging (DW-MRI) as a noninvasive tool to assess salivary gland function for follow-up of patients with radiation-induced xerostomia. This study included 23 patients with nasopharyngeal carcinoma who had been treated with parotid-sparing radiotherapy (RT). Salivary function was assessed by DW-MRI pre-treatment and one week and one year post-RT, respectively. The maximum apparent diffusion coefficient (ADC) of parotid glands (pADCmax) and the time to peak ADC of parotid glands (pTmax) during stimulation were obtained. Multivariate analysis was used to analyze factors correlated with the severity of radiation-induced xerostomia. The ADCs of parotid and submandibular glands (1.26 ± 0.10 × 10⁻³ mm²/s and 1.32 ± 0.07 × 10⁻³ mm²/s pre-RT, respectively) both showed an increase in all patients at one week post-RT (1.75 ± 0.16 × 10⁻³ mm²/s, p < 0.001 and 1.70 ± 0.16 × 10⁻³ mm²/s, p < 0.001, respectively), followed by a decrease in parotid glands at one year post-RT(1.57 ± 0.15 × 10⁻³ mm²/s, p < 0.001) but not in submandibular glands (1.69 ± 0.18 × 10⁻³ mm²/s, p = 0.581). An improvement in xerostomia was found in 13 patients at one year post-RT. Multivariate analysis revealed 4 significant predictors for the improvement of xerostomia, including dose to parotid glands (p = 0.009, odds ratio [OR] = 0.639), the ADC of submandibular glands (p = 0.013, OR = 3.295), pADCmax (p = 0.024, OR = 0.474), and pTmax (p = 0.017, OR = 0.729) at one week post-RT. The ADC value is a sensitive indicator for salivary gland dysfunction. DW-MRI is potentially useful for noninvasively predicting the severity of radiation-induced xerostomia