Patient dosimetry assessment with the somatostatin receptor antagonist <sup>68</sup>Ga-labelled OPS202 in the first clinical study of gastroenteropancreatic neuroendocrine tumors (GEP-NET) — ASN Events
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  3. Patient dosimetry assessment with the somatostatin receptor antagonist 68Ga-labelled OPS202 in the first clinical study of gastroenteropancreatic neuroendocrine tumors (GEP-NET)

Patient dosimetry assessment with the somatostatin receptor antagonist 68Ga-labelled OPS202 in the first clinical study of gastroenteropancreatic neuroendocrine tumors (GEP-NET) (#67)

Seval Beykan 1 , Guillaume P Nicolas 2 , Melpomeni Fani 2 , Uta Eberlein 1 , Ramon Mena 3 , Jens Kaufmann 3 , Hakim Bouterfa 3 , Romain Bejot 3 , Damian Wild 2 , Michael Lassmann 1
  1. Department of Nuclear Medicine, University of Würzburg, Würzburg, Germany
  2. Division of Nuclear Medicine, University of Basel Hospital, Basel, Switzerland
  3. OctreoPharm Sciences GmbH, Ipsen Group, Berlin, Germany

Objectives: Radiolabeled somatostatin receptor antagonists are a promising class of radiotracers for imaging of neuroendocrine tumor patients. We report on the biodistribution and dosimetry of 68Ga-OPS202 PET/CT in GEP-NET in a phase I trial (ClinicalTrials.gov NCT02162446).

Methods: In-vivo patient studies in metastatic G1/G2 GEP-NET patients (5f/7m, weight: 55±19kg) were performed with approximately 158±34 MBq 68Ga-OPS202 (amount of peptide: 15μg). Biodistribution and dosimetry of 68Ga-OPS202 were investigated. A series of whole-body PET/CT scans were conducted, multiple blood/urine samples were taken up to 4 hours after intravenous injection. Time-activity curves (TACs) were generated for blood and selected organs delineated on fused PET/CT images. Organ-specific time-integrated activity coefficients (TIACs) were calculated by using the NUKFIT software tool. Blood and image-based (LV2-LV4) time-activity curves were integrated to calculate the bone marrow TIACs. Based on these data, the absorbed organ dose coefficients for a 74kg patient were calculated using OLINDA/EXM. The ICPR60 weighting factors were applied to calculate the effective dose.

Results: The highest calculated absorbed doses were in urinary bladder wall (1.01E-01mGy/MBq), the kidneys (8.43E-02mGy/MBq) and the spleen (6.02E-02mGy/MBq). The mean absorbed dose for the bone marrow was 1.13E-02mGy/MBq. An analysis of the activity in the urine samples shows that 8.1±2.8% of the injected activity (range 3.3%-12.4%) and 1.6±0.6% of the injected activity (range 0.6%-2.6%) are excreted 2h and 4h, respectively, after administration. The effective dose coefficient for 68Ga-OPS202 is 2.4E‑02mSv/MBq which is comparable to previous studies with 68Ga-DOTATATE, 68Ga-DOTATOC, and lower than the values for 111In-DTPA-octreotide (8.0E-02mSv/MBq). The effective dose for 150 MBq of 68Ga-OPS202 is 3.6mSv.

Conclusion: 68Ga-OS202 is well tolerated and exhibits a favorable dosimetry delivering absorbed doses to organs that are comparable to other 68Ga-labeled somatostatin receptor agonist ligands. As expected, the main pathway of excretion is the urinary tract.