Long-term retention of 177Lu/177mLu-Dotatate in patients investigated by gamma spectrometry and gamma camera imaging.

Dosimetry in peptide receptor radionuclide therapy using (177)Lu-Dotatate is based on patient imaging during the first week after administration, and determination of the activity retention as a function of time for different tissues. For calculation of the absorbed dose it is generally assumed that the long-term activity retention follows the pattern determined from the first week. This work aims to investigate the validity of this assumption by performing additional patient measurements between 5 and 10 weeks after administration. A further aim is to investigate to what extent absorbed dose values are affected when including these measurements, also taking into account the radionuclide impurity of (177)mLu and build-up of secondary (177)Lu from the (177)mLu decay.