Comparison of amide proton transfer imaging and methionine PET for differentiating radiation necrosis and tumor recurrence after radiotherapy: A preliminary case series

Differentiating radiation necrosis from tumor recurrence after radiotherapy remains a significant clinical challenge in patients with metastatic brain tumors and directly influences treatment decisions. Although methionine positron emission tomography (PET) has demonstrated diagnostic utility, its cost and limited availability restrict routine clinical use. Amide proton transfer (APT) imaging is a noninvasive MRI-based technique that reflects tissue protein content and may provide complementary diagnostic information. This retrospective case series included 4 patients (5 lesions) with metastatic brain tumors who underwent both APT imaging and methionine PET for lesions suspicious for recurrence. An APT signal intensity ≥2.5%, derived from previously reported glioblastoma data, was used to define tumor recurrence. Among the 5 lesions, one was diagnosed as radiation necrosis and 4 as tumor recurrence. APT imaging demonstrated complete diagnostic concordance with methionine PET in all cases. Final diagnoses were established based on imaging findings and clinical follow-up without additional histopathological confirmation. In this small retrospective series, APT imaging showed findings concordant with methionine PET in differentiating radiation necrosis from tumor recurrence following radiotherapy. Although limited by sample size and lack of histopathological confirmation, these results suggest that APT imaging may serve as a useful complementary imaging modality in the post-radiotherapy setting.