Evaluation of L-3-[I-123]iodo-alpha-methyltyrosine SPET and [F-18]fluorodeoxyglucose PET in the detection and grading of recurrences in patients pretreated for gliomas at follow-up: a comparative study with stereotactic biopsy

Based on the results of stereotactic biopsy, we evaluated in a prospective fashion the efficiency of L-3-[I-123]iodo-alpha-methyltyrosine-single-photo n emission tomography (SPET) and [F-18]fluorodeoxyglucose (FDG) positron em ission tomography (PET) in the detection and grading of recurrences in pati ents previously treated for gliomas, The patient population comprised 30 in dividuals, nine with astrocytomas of grade II, ten with astrocytomas of gra de IV, three with oligoastrocytomas of grade II, six with oligodendroglioma s of grade II and two with anaplastic oligodendrogliomas of grade III) susp ected of recurrence and scheduled for further treatment. IMT SPET data were acquired using either by dual-or a triple-headed SPET camera, Multispect 2 /3. FDG uptake was measured with an ECAT ART PET camera. Two independent ob servers classified PET and SPET images as positive or negative for tumour t issue. Uptake of FDG and IMT was evaluated visually and, in the case of IMT , also quantitatively by calculating the ratios between tracer accumulation in the lesion and the unaffected contralateral regions of reference using the region of interest (ROI) technique. The PET and SPET results were compa red with the histopathological findings obtained either by stereotactic bio psy or in one case by open surgery. Glucose metabolism and amino acid uptak e of recurrences of brain tumours as assessed by FDG-PET and IMT-SPET corre lated highly with the histopathological findings, Based on the histopatholo gical data, FDG-PET and IMT-SPET findings confirmed recurrence in all cases of high-grade gliomas (IV). A difference could be demonstrated in low-grad e (II-III) tumour recurrences. True-positive IMT-SPET results were found in 86% of grade III and 75% of grade II recurrences, whereas FDG-PET yielded a sensitivity of 71% in tumours of grade III and 50% in those of grade II. With respect to the grade of malignancy of brain tumours at recurrence, IMT -SPET, in contrast to FDG-PET, does not permit adequate in vivo grading of nonmixed brain tumours of astrocytic or oligodendroglial origin. However, i n this study FDG-PET did not permit discrimination between upgrading of low -grade oligoastrocytomas (II) into anaplastic oligodendrogliomas (III) and upgrading into glioblastomas (IV) The results of this study indicate that F DG-PET and IMT-SPET are equivalent to stereotactic biopsy in their ability to identify high-grade tumours at recurrence. IMT-SPET proved to be superio r to FDG-PET in confirming low-grade recurrences. In the case of suspected progression of the grade of malignancy in ordinary gliomas, FDG-PET correla ted significantly with the histopathological grading, whereas IMT-SPET did not. However, tumour grading by FDG-PET has a limitation in mixed brain tum ours in that it is not possible to discriminate between progression of the oligo- versus the astrocytic tumour entity. In this case histopathological evaluation of the tumour grade remains necessary.