Operated low grade astrocytomas: a long term PET study on the effect of radiotherapy

The role of postoperative radiotherapy in patients with low grade gliomas i s not established yet. PET with C-11 methionine (MET) and F-18 fluorodeoxyg lucose (FDG) was used to perform cross sectional comparisons as well as wit hin patient follow up studies in 30 operated patients with fibrillary astro cytoma WHO II. Uptake of tracer by tumour was quantified by radio-activity concentration ratios in tumour over contralateral brain (T/C). Comparing pa tients who did (n=13) or did not (n=17) receive external radiotherapy subse quent to first tumour resection, no differences in MET and FDG T/C between both groups were found during a postoperative period of 94 months (when rec urrence and malignant progression of low grade astrocytomas are expected). Malignant progression occurred at a similar rate in both patient groups at a mean (SD) postoperative interval of 46 (26) months. Irrespective of wheth er radiotherapy was applied or not, malignant tumour recurrences showed hig her T/C values (MET: 1.70 (0.64), FDG: 0.98 (0.23)) than recurrences withou t signs of malignancy (MET: 1.21 (0.21), FDG: 0.82 (0.08)) (Mann-Whitney: M ET p=0.086, FDG p=0.035). The data show a relative lack of radiotherapy adm inistered immediately after first tumour resection. In the course of diseas e, patients with tumours undergoing malignant progression may be identified with PET tracer methods.