Diagnostic criteria for RTLI

The diagnostic criteria for RTLI were as follows: (i) white matter lesions (finger-like lesions of increased signal intensity in T2-weighted (T2-w) images); (ii) contrast-enhanced lesions (lesions with or without necrosis in contrast-enhanced T1-weighted (CET1-w) images with heterogeneous signal abnormalities in T2-w images); and (iii) cysts (round or oval-shaped well-defined lesions of very high signal intensity in T2-w images with thin or imperceptible walls). Differential diagnosis was performed to ensure that the changes were not due to other factors, such as tumor recurrence. The latency of RTLI was measured from the day of radiotherapy completion to the date of MRI diagnosis. After completing radiotherapy, all the patients underwent regular follow-up during the latent period, as described in the inclusion criteria. Nasopharyngeal mirror, endoscopic, physical examinations, as well as MRI, were performed during the follow-up period. All MRI images were retrospectively reviewed by two independent radiologists (with 10 and 20 years of experience in NPC, respectively), and disagreements were resolved by consensus.