Non invasive determination of IDH mutation status in high-grade gliomas: utility of ADC maps and (18F)-DOPA PET/ TC

Aim The brain tumors new classification (2016 WHO) distinguishes diffuse gliomas based on the molecular characteristics of isocitrate dehydrogenase (IDH) in IDH-mutated, IDH-wild type (WT) and not otherwise specified. The evaluation of IDH mutation status has diagnostic, prognostic and therapeutic implications. The aim of this study is to evaluate whether the analysis of ADC maps and (18F-DOPA) can non-invasively predict the IDH mutation status. Conventional MRI and ADC maps of 16 patients (11-M, 5-F) with histological diagnosis of high-grade diffuse glioma GIII, GIV and the evaluation of IDH mutation status (9-MUT, 7-WT), were retrospectively evaluated. Methods All MRI were performed on a 1.5T MR scan (GE-optima 450). In order to place the ROIs on the solid components of the lesion, the ADC maps were elaborated and co-registered with the T2w and c.e.T1w images. The ADC-mean values were calculated, choosing the lowest values for each patient. The same procedure was performed with PET/CT scan using (18F)-DOPA as tracer. We placed (VOIs) in the same area where was applied the ROIs in RM scan in both groups of patients in order to calculate the SUV-mean values between IDH-MUT and IDH-WT. To compare the ADCmean and SUVmean values between IDH-MUT and IDH-WT performing Student's "t" test, considering significant value of p <0.05 in both groups. Results The ADCmean values in IDH-WT patients (0.86x10-3mm2/s ± 0.06)were lower than those of IDH-MUT patients (1.24x10-3mm2 /s ±0.19) with difference between the two groups significant for p<0.01. The value of ADC ≥ 1.01 x10-3mm2/s can be considered asa "cut-off" to differentiate them mutation status. The ratio between tumor uptake to background in PET/CT scan in IDH-WT group was (2.59x10-3mm2/s ± 0,448), higher than in IDH-MUT group (1.9x10-3mm2/s ± 0,533), with a significative p<0,05. Conclusion In the standard routine MR and PET are already assested to evaluate brain tumors but they are both of limited value if advanced techniques are not applied and if there is no integration of anatomical and functional data. In our experience adding quantitative data such as ADC to conventional MR and semi-quantitative analysis to PET with aminoacid tracers like DOPA is necessary for a better comprehension of tumor nature. In the era of molecular imaging this is a novel approach that could be introduced as a non-invasive marker of specific genomic patterns.