PET SUV correlates with radionuclide uptake in peptide receptor therapy in meningioma

To investigate whether the tumour uptake of radionuclide in peptide receptor radionuclide therapy (PRRT) of meningioma can be predicted by a PET scan with 68Ga-labelled somatostatin analogue. In this pilot trial, 11 meningioma patients with a PET scan indicating somatostatin receptor expression received PRRT with 7.4 GBq 177Lu-DOTATOC or 177Lu-DOTATATE, followed by external beam radiotherapy. A second PET scan was scheduled for 3 months after therapy. During PRRT, multiple whole-body scans and a SPECT/CT scan of the head and neck region were acquired and used to determine the kinetics and dose in the voxel with the highest radionuclide uptake within the tumour. Maximum voxel dose and retention of activity 1 h after administration in PRRT were compared to the maximum standardized uptake values (SUVmax) in the meningiomas from the PET scans before and after therapy. The median SUVmax in the meningiomas was 13.7 (range 4.3 to 68.7), and the maximum fractional radionuclide uptake in voxels of size 0.11 cm3 was a median of 23.4 x 10-6 (range 0.4 x 10-6 to 68.3 x 10-6). A strong correlation was observed between SUVmax and the PRRT radionuclide tumour retention in the voxels with the highest uptake (Spearman's rank test, P < 0.01). Excluding one patient who showed large differences in biokinetics between PET and PRRT and another patient with incomplete data, linear regression analysis indicated significant correlations between SUVmax and the therapeutic uptake (r = 0.95) and between SUVmax and the maximum voxel dose from PRRT (r = 0.76). Observed absolute deviations from the values expected from regression were a median of 5.6 x 10-6 (maximum 9.3 x 10-6) for the voxel fractional radionuclide uptake and 0.40 Gy per GBq (maximum 0.85 Gy per GBq) 177Lu for the voxel dose from PRRT. PET with 68Ga-labelled somatostatin analogues allows the pretherapeutic assessment of tumour radionuclide uptake in PRRT of meningioma and an estimate of the achievable dose. (orig.)