[The quantitative evaluation of early radiation-induced changes in the salivary glands using MRI]

Objective: To quantitatively evaluate the early radiation injury of salivary glands in patients with nasopharyngeal carcinoma (NPC) after intensity-modulated radiotherapy (IMRT). Methods: Twenty patients with NPC between 2014 and 2015 from the Second Affiliated Hospital of Soochow University were retrospectively analyzed.All patients underwent an MRI scan before and after IMRT.The volumes, T(1)WI, T(2)WI signal intensity(SIs) and apparent diffusion coefficient (ADCs) of the parotid and submandibular glands were measured.The relative signal intensity (RSIs) of each salivary gland was calculated with cerebrospinal fluid as control.The quantitative parameters of salivary glands were compared before and after radiotherapy. Results: The volumes (cm(3)) and T(1)WI RSIs of the parotid and submandibular glands (14.88±6.00, 5.21±1.76, 2.98±1.05, 1.88±0.42, respectively) were significantly lower than those before radiotherapy (22.26±8.26, 7.76±2.45, 3.58±1.02, 2.27±0.50, respectively) (t=9.921, 4.013, 10.126, 4.202, respectively, P=0.000 for all). The T(2)WI RSIs and ADCs (×10(-3) mm(2)/s) of the parotid and submandibular glands (0.50 ± 0.08, 0.41±0.04, 1.31±0.19, 1.50±0.13, respectively) were significantly higher than those before radiotherapy (0.45±0.07, 0.33±0.05, 1.02±0.21, 1.23±0.13, respectively) (t=-4.846, -9.276, -9.957, -10.679, respectively, P=0.000 for all). The volumes of parotid and submandibular glands were correlated with ADCs (r=-0.512, P=0.000; r=-0.358, P=0.001; respectively). The volumes and ADCs of submandibular glands were correlated with T(1)WI RSIs and T(2)WI RSIs(P<0.05). Conclusion: MRI can quantitatively evaluate the early changes of salivary glands after radiotherapy of nasopharyngeal carcinoma as a noninvasive method, and has high clinical application potential.