Utility of F18-FET PET/MRI for differentiating treatment related changes from recurrence/ residual, prognostication and as a follow up modality in glioma

Fluorine-18-fluoro-ethyl-tyrosine (¹⁸F-FET), an amino acid radiotracer, is used in neuro-oncological positron emission tomography (PET) imaging. Its use is more significant in cases of high grade gliomas where MRI in inconclusive and in differentiating recurrence from treatment related changes. The study aims at observing the utility of ¹⁸F-FET simultaneous PET/ MRI over MRI. We have analyzed a data of 30 patients. All of them underwent ¹⁸F-FET PET/MRI at our centre. A radioactivity of 5-7mci (185-259 MBq) was injected. The Scans were performed 30 minutes post injection. Standard MRI sequences were added like 3D FLAIR, T1-MPRAGE. PET imaging reconstruction was done using iterative reconstruction with 512 matrix, 5 iterations, FWHM-2. The standard uptake value (SUV) and tumor to background (TBR) was calculated in all the case for analysis. Results: We analyzed a heterogeneous data of 30 patients, 20 females and 10 males, histopathological classification of tumor was done and showed in the Table 1. All the cases were post-operative. FET-PET showed increased radiotracer uptake in 27 cases. 3 cases showed no radiotracer uptake on PET. There was concordance noted in 28 cases between PET and MRI findings and discordance noted in 2 cases where PET findings were suggestive of recurrence and MRI findings suggestive of post-operative changes. Three cases had multiple PET/MRI scans available over multiple time points, where no recurrence was noted in either PET or MRI. Out of 30 cases, 24 cases were of high-grade tumors (III/IV), 3 were low grade I/ II and in 3 cases grade was not specified. In high grade tumor, SUVmax was greater than 2.5 and TBR greater then 2.0 (except two cases). In low-grade tumors, two of the cases showed a SUV of < 2.5 and TBR <2.0 while two shoed higher than this. From the above data analysis, it can be concluded that, (¹⁸F)FET PET/MRI is superior to (¹⁸F)FDG (in view of low background in ((¹⁸F)FET) and MRI in differentiating post operative changes from recurrence/residual disease. ¹⁸F-FET can be used for following up studies of the same. Simultaneous (¹⁸F)-FET-PET-MR adds on to the diagnostic value and can be a useful tool as well to ascertain the grade of tumors hence can be valuable in prognostication though it needs larger sample size to further validate the study. (author)