Discrimination between (high-grade) brain tumor recurrence and radiation necrosis (RN) remains a diagnostic challenge because both entities have similar imaging characteristics on conventional magnetic resonance imaging (MRI). Metabolic imaging, such as positron emission tomography (PET) could overcome this diagnostic dilemma. In this study, we investigated the potential of 2-[18F]-fluoro-2-deoxy-D-glucose (18F-FDG), O-(2-[18F]-fluoroethyl)-L-tyrosine (18F-FET), and [18F]-Fluoromethyl-dimethyl-2-hydroxyethylammonium (18F-fluoromethylcholine, 18F-FCho) PET in discriminating high-grade tumor from RN.
We developed a glioblastoma (GB) rat model by inoculating F98 GB cells into the right frontal region. Induction of RN was achieved by irradiating the right frontal region with 60 Gy using three arcs with a beam aperture of 3 × 3 mm (n = 3). Dynamic PET imaging with 18F-FDG, 18F-FET, and 18F-FCho, as well as 18F-FDG PET at a delayed time interval (240 min postinjection), was acquired.
MRI revealed contrast-enhancing tumors at 15 days after inoculation (n = 4) and contrast-enhancing RN lesions 5–6 months postirradiation (n = 3). On 18F-FDG PET, the mean lesion-to-normal ratio (LNRmean) was significantly higher in GB than in RN (p = 0.034). The difference in the LNRmean between tumors and RN was higher on the late 18F-FDG PET images than on the PET images reconstructed from the last time frame of the dynamic acquisition (this is at a conventional time interval). LNRs obtained from 18F-FCho PET were not significantly different between GB and RN (p = 1.000). On 18F-FET PET, the LNRmean was significantly higher in GB compared to RN (p = 0.034).
Unlike 18F-FCho, 18F-FDG and 18F-FET PET were effective in discriminating GB from RN. Interestingly, in the case of 18F-FDG, delayed PET seems particularly useful.
Advances in knowledge and implications for patient care
Our results suggest that (delayed) 18F-FDG and 18F-FET PET can be used to discriminate GB (recurrence) from RN. Confirmation of these results in clinical studies is needed.
Julie Bolcaen, Benedicte Descamps, Karel Deblaere, Tom Boterberg, Filip De Vos Pharm, Jean-Pierre Kalala, Caroline Van den Broecke, Elke Decrock, Luc Leybaert, Christian Vanhove & Ingeborg Goethals.