A prospective trial of dynamic contrast-enhanced MRI perfusion and fluorine-18 FDG PET-CT in differentiating brain tumor progression from radiation injury after cranial irradiation

Abstract

Background: The aim of this study was to assess the effectiveness of fluorine-18 fluorodeoxyglucose (FDG) PET-CT and dynamic contrast-enhanced (DCE) MRI in differentiating tumor progression and radiation injury in patients with indeterminate enhancing lesions after radiation therapy (RT) for brain malignancies.

Methods: Patients with indeterminate enhancing brain lesions on conventional MRI after RT underwent brain DCE-MRI and PET-CT in a prospective trial. Informed consent was obtained. Lesion outcomes were determined by histopathology and/or clinical and imaging follow-up. Metrics obtained included plasma volume (Vp) and volume transfer coefficient (K(trans)) from DCE-MRI, and maximum standardized uptake value (SUVmax) from PET-CT; lesion-to-normal brain ratios of all metrics were calculated. The Wilcoxon rank sum test and receiver operating characteristic analysis were performed.

Results: The study included 53 patients (29 treated for 29 gliomas and 24 treated for 26 brain metastases). Progression was determined in 38/55 (69%) indeterminate lesions and radiation injury in 17 (31%). Vpratio (VP lesion/VP normal brain, P < .001), K(trans) ratio (P = .002), and SUVratio (P = .002) correlated significantly with diagnosis of progression versus radiation injury. Progressing lesions exhibited higher values of all 3 metrics compared with radiation injury. Vpratio had the highest accuracy in determining progression (area under the curve = 0.87), with 92% sensitivity and 77% specificity using the optimal, retrospectively determined threshold of 2.1. When Vpratio was combined with K(trans) ratio (optimal threshold 3.6), accuracy increased to 94%.

Conclusions: Vpratio was the most effective metric for distinguishing progression from radiation injury. Adding K(trans) ratio to Vpratio further improved accuracy. DCE-MRI is an effective imaging technique for evaluating nonspecific enhancing intracranial lesions after RT.

Keywords: 18F-FDG PET-CT; DCE MRI perfusion; radiation injury.

Fig. 1.

Receiver operating characteristic (ROC) analysis for Vp_ratio, K^trans_ratio, and SUV_ratio demonstrating the optimal cutoffs to be 2.1, 3.6, and 1.2, respectively, in distinguishing between progression and radiation injury.

Fig. 2.

Patient example of tumor progression detected by DCE-MRI perfusion. Images obtained in a 30-year-old man with metastatic sarcoma who underwent SRS to a left parietal lobe metastasis. Axial contrast-enhanced T1-weighted image before treatment (A) shows an enhancing mass (arrow) that increases in size 6 months after treatment (B). Vp map of the enlarging mass (C) demonstrates increased perfusion; however, PET-CT showed no abnormal FDG uptake (D). Pathology confirmed progression.

Fig. 3.

Patient example of radiation injury detected by DCE-MRI perfusion and PET-CT. Images obtained in a 39-year-old woman with metastatic breast cancer who underwent SRS to a left frontal lobe metastasis. Axial contrast-enhanced T1-weighted image (A) demonstrates an enhancing mass that had increased in size 1 year after SRS (arrow). DCE-MRI showed no increase in perfusion on the Vp map (B) and no increase in SUV on PET-CT (C). The lesion remained stable 1 year after it had enlarged (D) without any additional therapy and was determined to represent radiation injury.