title: Evaluation of two intraoperative gamma detectors for assessment of177Lu activity concentration in vivo.
abstract: BACKGROUND
  Patients with somatostatin receptor-expressing neuroendocrine tumours can be treated with intravenously administered177Lu-octreotate. Few patients are cured with the present protocol due to the current dose limitation of normal organs at risk, such as the kidneys. By locally administering177Lu-octreotate to the liver for the purpose of treating liver metastases, a substantially reduced absorbed dose to organs at risk could be achieved. The development of such a technique requires the capability of measuring the177Lu activity concentration in tissues in vivo. The aim of this study was to evaluate different performance parameters of two commercially available intraoperative gamma detectors in order to investigate whether intraoperative gamma detector measurements could be used to determine177Lu activity concentration in vivo.
  
  
  RESULTS
  Measurements were made using different sources containing177Lu. Response linearity, sensitivity, spatial resolution and its depth dependence, organ thickness dependence of the measured count rate and tumour detectability were assessed for two intraoperative gamma detectors. The two detectors (a scintillation and a semiconductor detector) showed differences in technical performance. For example, the sensitivity was higher for the scintillation detector, while the spatial resolution was better for the semiconductor detector. Regarding organ thickness dependence and tumour detectability, similar results were obtained for both detectors, and even relatively small simulated tumours of low tumour-to-background activity concentration ratios could be detected.
  
  
  CONCLUSIONS
  Acceptable results were obtained for both detectors, although the semiconductor detector proved more advantageous for our purpose. The measurements demonstrated factors that must be corrected for, such as organ thickness or dead-time effects. Altogether, intraoperative gamma detector measurements could be used to determine177Lu activity concentration in vivo.
authors.affiliation: Department of Radiation Physics, Institute of Clinical Sciences, Sahlgrenska Cancer Center, Sahlgrenska Academy, University of Gothenburg, SE-413 45, Gothenburg, Sweden. viktor.sandblom@gu.se.
authors.forename: Viktor
authors.identifier: http://orcid.org/0000-0002-0652-3342
authors.initials: V
authors.lastname: Sandblom
authors.affiliation: Department of Radiation Physics, Institute of Clinical Sciences, Sahlgrenska Cancer Center, Sahlgrenska Academy, University of Gothenburg, SE-413 45, Gothenburg, Sweden.
authors.forename: Ingun
authors.initials: I
authors.lastname: Ståhl
authors.affiliation: Department of Surgery, Institute of Clinical Sciences, Sahlgrenska Cancer Center, Sahlgrenska Academy, University of Gothenburg, SE-413 45, Gothenburg, Sweden.
authors.forename: Roger
authors.initials: R
authors.lastname: Olofsson Bagge
authors.affiliation: Department of Radiation Physics, Institute of Clinical Sciences, Sahlgrenska Cancer Center, Sahlgrenska Academy, University of Gothenburg, SE-413 45, Gothenburg, Sweden.
authors.forename: Eva
authors.initials: E
authors.lastname: Forssell-Aronsson
keywords: 177Lu; Intraoperative gamma detectors; Neuroendocrine tumours; Performance evaluation