Early Changes of Irradiated Parotid Glands Evaluated by T1rho-Weighted Imaging: A Pilot Study

Objective: The aim of the study was to confirm the feasibility of T1rho-weighted imaging to evaluate the dynamic changes of parotid glands in patients with nasopharyngeal carcinoma (NPC) undergoing intensity-modulated radiation therapy.

Methods: Twenty-six NPC patients (19 men; 7 women; mean [SD] age, 48.9 [13.4] years) underwent the following 3 serial T1rho-weighted imaging: within 2 weeks before radiotherapy (RT, pre-RT), 5 weeks after the beginning of RT (mid-RT), and 4 weeks after RT (post-RT). Parotid volumes, T1rho values, mean radiation doses, and xerostomia degrees were recorded. Change rates of parotid T1rho values were correlated with parotid atrophy rates, mean radiation doses, and xerostomia degrees.

Results: During RT, parotid volume decreased (atrophy rate, 32.7 [8.1%] at mid-RT and 27.9 [10.0%] at post-RT compared with pre-RT; both P < 0.001) and parotid T1rho values increased (change rate, 25.0 [15.8%] at mid-RT and 30.1 [18.0%] at post-RT compared with pre-RT, both P < 0.001) significantly. The change rate of parotid T1rho value correlated with the atrophy rate significantly at post-RT (r = 0.301, P = 0.047). Intraobserver and interobserver reproducibility of parotid T1rho measurements were excellent (intraclass correlation coefficient, 0.974 and 0.956, respectively).

Conclusions: Dynamic changes of radiation-induced parotid damage in NPC patients who underwent intensity-modulated radiation therapy could be noninvasively evaluated by T1rho-weighted imaging.