O7.05 * DIFFERENTIATION OF LOCAL RECURRENT BRAIN METASTASIS FROM RADIATION-INDUCED CHANGES USING O-(2-[18F]FLUOROETHYL)-L-TYROSINE PET

Abstract

BACKGROUND: The aim of this study was to investigate the potential of O-(2-[18F]fluoroethyl)-L-tyrosine (18F-FET) PET for differentiating local recurrent brain metastasis from radiation-induced changes after radiation therapy since the use of contrast-enhanced MRI for this issue is often difficult. METHODS: 38 patients (mean age, 54 ± 11 y) with single or multiple contrast-enhancing brain lesions (n = 49) on MRI after radiation therapy of brain metastases were investigated with dynamic 18F-FET PET. Maximum and mean tumor/brain ratios (20-40 min postinjection) (TBRmax, TBRmean) of 18F-FET uptake were determined. Time activity curves (TAC) were generated and the time-to-peak (TTP) was calculated. Furthermore, TACs of each lesion were assigned to one of the following curve patterns: (I) constantly increasing 18F-FET uptake; (II) 18F-FET uptake peaking early (TTP ≤ 20 min) followed by a plateau; and (III) 18F-FET uptake peaking early (TTP ≤ 20 min) followed by a constant descent. The diagnostic accuracy of the TBRmax and TBRmean of 18F-FET uptake and the curve patterns for the correct identification of recurrent brain metastasis was evaluated by receiver-operating-characteristic (ROC) analyses using subsequent histological analysis (17 lesions in 16 patients) or clinical course and MR imaging findings (32 lesions in 22 patients) as reference. RESULTS: Both TBRmax and TBRmean were significantly higher in patients with recurrent metastasis (n = 25) than in patients with radiation-induced changes (n = 24) (TBRmax 3.3 ± 1.0 vs. 2.3 ± 0.4, P < 0.001; TBRmean 2.2 ± 0.4 vs. 1.7 ± 0.1, P < 0.001). The sensitivity/specificity of 18F-FET PET for the correct identification of recurrent brain metastases was 84 / 79% using TBRmax (area under the curve, 0.851 ± 0.06, cut-off 2.6; P < 0.001), 92/83% using TBRmean (area under the curve, 0.901 ± 0.05, cut-off 1.9; P < 0.001), and 84/100% for curve patterns II and III vs. curve pattern I (P < 0.001). Highest sensitivity/specificity (96/88%) to diagnose local recurrent metastasis was obtained when both a TBRmean ≥1.9 and curve pattern II or III were present (area under the curve, 0.963 ± 0.03; P < 0.001). CONCLUSION: Our findings suggest that the combined evaluation of the TBRmean of 18F-FET uptake and the pattern of TAC can differentiate local brain metastasis recurrence from radiation-induced changes with high accuracy. 18F-FET PET may thus contribute significantly to the management of patients with brain metastases.