Potential Predictive Value of Intravoxel Incoherent Motion Magnetic Resonance for Xerostomia of Nasopharyngeal Carcinoma

Xerostomia, caused by radiation-induced parotid damage, is the most commonly reported complications of radiotherapy (RT) to nasopharyngeal carcinoma (NPC). This study aimed to evaluate the value of IVIM MR in monitoring radiation parotid gland damage and predicting the risk of xerostomia.A total of 54 patients were enrolled and underwent IVIM MR scans at before RT, after the fifth fraction, halfway through the course of RT, and at the end of radiotherapy. The parameters of IVIM MR include pseudo-diffusion coefficient (D*), perfusion fraction (f), and pure diffusion coefficient (D). The degree of xerostomia in NPC patients was assessed before each MR examination using the acute radiation morbidity scoring criteria proposed by the Radiation Therapy Oncology Group (RTOG). Concurrently, the time when the patient first reported suffering from xerostomia was recorded. The IVIM parameters trend throughout the RT, and the relationships between IVIM parameters and xerostomia, were analyzed.All of the IVIM parameters increased from pre-RT to post-RT significantly (all p < 0.001). The increase rate of D from pre-RT to halfway through the RT was 32.61%, which was significantly higher than 15.64% from halfway to post-RT (p<0.001), indicating that cell necrosis in the first half of treatment is significantly higher than that in the second half. Both D* and F had significantly increased from pre-RT to halfway through the radiotherapy (p<0.001), with an increase rate of 19.58% and 29.38%, respectively. However, no significant increase was observed from Halfway to post-RT (p>0.05), with an increase rate of 4.10% and 8.30%, respectively. This may be due to radiation-induced vasculitic dilation that is significant in the first half of the radiotherapy but plateaus in the second half. Pre-D (OR = 23.85; 95% CI = 2.39, 237.82; p = .007) and pre-D* (OR = 0.75; 95% CI = 0.63, 0.91; p = 0.003) are independent influencing factors for xerostomia at 3 months after the completion of RT. D and F were significantly higher after the fifth fraction compared with Pre-RT (both p<0.05), respectively increased 31.25% and 25.16%. D* increase by 15% (p = 0.081). IVIM scans can assess parotid gland damage early. And the average time of parotid damage underwent IVIM scan was 5.99 ± 0.84 (day), much earlier than 11.84 ± 2.74 (day) according to RTOG.Our study indicates that IVIM MR can dynamically monitor radiotherapy-induced parotid gland damage, and much earlier and objectively than RTOG.