The SPECT compound 57 Co-DOTATOC has recently been shown to have the highest affinity ever found for somatostatin receptor subtype 2. Moreover, the internalization rate into the tumour cell line AR42J was also the highest found for any somatostatin-based radiopharmaceutical. We here present a method to prepare the positron emission tomography compound 55 Co-DOTATOC as a new promising radiopharmaceutical for positron emission tomography via solid target irradiations of enriched Fe-metal. Also, the new, potent Auger-electron-emitting radioisotope 58mCo and the resulting therapeutic compound 58m Co-DOTATOC as candidate for targeted radionuclide therapy of somatostatin receptor-positive tumours have been prepared with high yield and high radiochemical purity.

Background Kidney dosimetry after peptide receptor radionuclide therapy using 177Lu-labelled somatostatin analogues is a procedure with multiple steps. We present the SPECT/CT-based implementation at Aarhus University Hospital and evaluate the uncertainty of the various steps in order to estimate the total uncertainty and to identify the major sources of uncertainty. Absorbed dose data from 115 treatment fractions are reported. Results The total absorbed dose with uncertainty is presented for 59 treatments with [177Lu]Lu-DOTATOC and 56 treatments with [177Lu]Lu-DOTATATE. For [177Lu]Lu-DOTATOC the mean and median specific absorbed dose (dose per injected activity) is 0.37 Gy/GBq and 0.38 Gy/GBq, respectively, while for [177Lu]Lu-DOTATATE the median and mean are 0.47 Gy/GBq and 0.46 Gy/GBq, respectively. The uncertainty of the procedure is estimated to be about 13% for a single treatment fraction, where the absorbed dose calculation is based on three SPECT/CT scans 1, 4 and 7 days post-injection, while it increases to about 19% if only a single SPECT/CT scan is performed 1 day post-injection. Conclusions The specific absorbed dose values obtained with the described procedure are comparable to those from other treatment sites for both [177Lu]Lu-DOTATOC and [177Lu]Lu-DOTATATE, but towards the lower end of the range of reported values. The estimated uncertainty is also comparable to that from other reports and judged acceptable for clinical and research use, thus proving the kidney dosimetry procedure a useful tool. The greatest reduction in uncertainty can be obtained by improved activity determination, partial volume correction and additional SPECT/CT scans.