Pilot study: uptake of [18F]FLT and [18F]FDG in neurofibromatosis type II patients with vestibular schwannomas.

Objectives To investigate whether a quantifiable signal can be detected with [18F]fluorothymidine ([18F]FLT) and/or [18F]fluorodeoxyglucose ([18F]FDG) positron emission tomography (PET) imaging in neurofibromatosis type II (NF2) patients with vestibular schwannomas (VS) and whether these measurements differentiate tumour growth.

Methods Six patients with NF2 VSs, (5/6 bilateral with a total of 11 lesions), were scanned. Based on routine clinical MRI volumetric assessment at two time points VS lesions were classified as rapid growing (RG) or non-rapid growing (NRG). Patients were injected with 200 MBq of [18F]FLT and [18F]FDG on two separate occasions and scanned on both a high resolution research tomograph (HRRT) dedicated brain scanner and a Siemens Biograph TrueV PET/CT. The scan sequence was 60-gap-30-gap-30 minutes with alternated order of scanners. For the purpose of this work we report the data for the clinically relevant TrueV, during scan 2 at approximately 75-105 minutes post injection and calculated either from direct measurement or from interpolation of data from scans 1 and 3. PET data was reconstructed with 10 minute frames without resolution modelling and with frame by frame image based motion correction. Lesions of contrast enhancement were manually segmented on previously acquired MRI data and used to obtain mean and maximum standardised uptake values (SUV) within these regions.

Results SUV mean and max at approximately 75-105 minutes after injection are shown in table 1 for contrast enhancing regions for both FDG and FLT. SUVs were obtained which were measurable above background. The mean (range) of SUV for FDG of 2.4 (0.7-4.6) for SUV mean and 5.0 (1.5-7.8) for SUV max. For FLT the values were 0.8 (0.2-1.3) for SUV mean and 2.1 (0.7-3.8) for SUV max. There is a general proportional relationship between SUVs for FDG and FLT with a FDG:FLT ratio of 2.8:1 (SUV mean) and 2.2:1 (SUV max) and with R2 values of 0.58 and 0.31. With both SUV mean and SUV max both FDG and FLT show good potential in the classification of rapidly growing lesions, with area under the receiver operator characteristic curve: for FDG of 0.85 (SUV mean) and 0.70 (SUV max); and for FLT of 0.95 (SUV mean) and 0.83 (SUV max).

Conclusions Data from these six patients indicate that both [18F]FLT and [18F]FDG show promise in the differentiation of rapidly growing lesions (recruitment still ongoing). Methodological challenges such as subject movement and spill-in from bone marrow and brain will be further investigated. Uptake patterns will also be compared to further MRI and clinical follow-up.

• Download figure
• Open in new tab
• Download powerpoint