title: Long-Term Retention of 177Lu/177mLu-DOTATATE in Patients Investigated by γ-Spectrometry and γ-Camera Imaging.
abstract: 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 aimed to investigate the validity of this assumption by performing additional patient measurements between 5 and 10 wk after administration. A further aim was to investigate to what extent absorbed dose values were affected when including these measurements, also taking into account the radionuclide impurity of (177m)Lu and build-up of secondary (177)Lu from the (177m)Lu decay.
  
  
  METHODS
  A combination of methods was used: planar γ-camera imaging as part of the clinical dosimetry protocol, determination of the whole-body activity between 5 and 9 wk after injection using spectrometric NaI(Tl) and HPGe detectors, and imaging between 5 and 10 wk after injection for assessment of the activity distribution. From these measurements the long-term retention of activity was determined and the relative influence on absorbed doses calculated.
  
  
  RESULTS
  The most important finding was a clearly visualized tumor uptake in images from between 5 and 7 wk after injection and in 1 patient also kidney and spleen uptake in images acquired on day 33. As a consequence, the total-body time-activity curve had a tail, which was not completely captured by imaging during the first week. The absorbed doses to total body and tumors obtained when including these late time points were on average 5%-6% higher than those obtained when using data acquired during the first week. The contributions to the absorbed dose from (177m)Lu and secondary (177)Lu were negligible.
  
  
  CONCLUSIONS
  At approximately 5-7 wk after injection, there was a measureable amount of (177)Lu-DOTATATE in patients, which is mainly governed by retention in tumors. For tumor dosimetry, imaging at a later time than the routinely used 7 d may be warranted. The contribution to the absorbed dose from the radionuclide impurity of (177m)Lu was negligible.
authors.affiliation: Department of Clinical Sciences Lund, Medical Radiation Physics, Lund University, Lund, Sweden katarina.sjogreen_gleisner@med.lu.se.
authors.forename: Katarina Sjögreen
authors.initials: KS
authors.lastname: Gleisner
authors.affiliation: Department of Clinical Sciences Lund, Medical Radiation Physics, Lund University, Lund, Sweden.
authors.forename: Gustav
authors.initials: G
authors.lastname: Brolin
authors.affiliation: Division of Oncology and Pathology, Department of Clinical Sciences Lund, Lund University, Lund, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Sundlöv
authors.affiliation: Department of Clinical Sciences Lund, Medical Radiation Physics, Lund University, Lund, Sweden ZERNIKE Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands; and.
authors.forename: Edita
authors.initials: E
authors.lastname: Mjekiqi
authors.affiliation: Department of Translational Medicine, Lund University, Lund, Sweden.
authors.forename: Karl
authors.initials: K
authors.lastname: Östlund
authors.affiliation: Division of Oncology and Pathology, Department of Clinical Sciences Lund, Lund University, Lund, Sweden.
authors.forename: Jan
authors.initials: J
authors.lastname: Tennvall
authors.affiliation: Department of Clinical Sciences Lund, Medical Radiation Physics, Lund University, Lund, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Larsson
mesh_terms: D005260:Female; D015902:Gamma Cameras; D005720:Gamma Rays; D006801:Humans; D007668:Kidney / Q000528:radiation effects; D008187:Lutetium / Q000737:chemistry; D008297:Male; D018358:Neuroendocrine Tumors / Q000175:diagnosis / Q000532:radiotherapy*; D015282:Octreotide / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D009942:Organometallic Compounds / Q000493:pharmacokinetics*; D019047:Phantoms, Imaging; D011868:Radioisotopes / Q000737:chemistry; D011874:Radiometry / Q000379:methods; D018000:Receptors, Peptide / Q000737:chemistry; D013053:Spectrophotometry / Q000379:methods*; D013154:Spleen / Q000528:radiation effects; D013997:Time Factors
chemical_list: D009942:Organometallic Compounds; D011868:Radioisotopes; D018000:Receptors, Peptide; D008187:Lutetium; C447941:lutetium Lu 177 dotatate; D015282:Octreotide
keywords: 177Lu; dosimetry; peptide receptor radiotherapy