Diagnostic accuracy of C-methionine PET in detecting neuropathologically confirmed recurrent brain tumor after radiation therapy.

Objective: This study aims to determine the diagnostic test accuracy (DTA) of C-methionine (MET) PET in the discrimination between recurrent tumor and radiation-induced injury in neuropathologically confirmed cases.

Methods: A retrospective cohort of 30 patients with previously irradiated intracranial tumors (23 gliomas, 6 metastases, and 1 meningioma) was included. All patients underwent a preoperative MET PET and postoperative neuropathological analysis. Maximum and mean standardized uptake values (SUV) were obtained in the lesion, in the contralateral mirror region, and in the contralateral frontal cortex. Lesion-to-background SUV ratios (SUR mirror and SUR cortex) were then calculated. The Mann-Whitney U test was used to evaluate differences in SUV ratios between confirmed recurrent tumor and radiation injury. DTA was determined through receiver operating characteristic (ROC) analysis.

Results: Twenty-one patients had recurrent tumor and nine had radiation injury. The area under the ROC curve (AUC) was 0.89 for SURmirror and 0.88 for SURcortex. The mean (SD) of SURmirror was 2.37 (0.58) in tumor recurrence and 1.57 (0.40) in radiation necrosis (P ≤ 0.001). The corresponding values for SURcortex were 2.13 (0.50) and 1.45 (0.37) (P = 0.001). Clinically relevant cutoffs were SURmirror ≥ 1.99 giving a specificity of 100% for tumor recurrence with a sensitivity of 76% and SURcortex ≥ 1.58 giving a sensitivity and specificity of 90 and 78%, respectively.

Conclusions: Based on neuropathologically confirmed cases, the DTA of SURmirror and SURcortex from C-methionine PET was high when discriminating recurrent tumor from radiation injury.