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ST: Strahlen- und Medizinphysik

ST 9: PET und CT

ST 9.2: Invited Talk

Tuesday, March 14, 2006, 14:50–15:10, D

Molecular Radiation Treatment Planning (MRTP) using receptor PET/CT - implications for radiopeptide therapy — •Richard P. Baum and Christiane Wehrmann — Zentralklinik Bad Berka, Dept. of Nuclear Medicine, Center for P.E.T., 99437 Bad Berka, Germany

Peptide receptor radionuclide therapy (PRRT) is used in our department since 6 years (approx. 750 applications) for the treatment of patients with metastatic neuroendocrine tumors. We introduced Ga-68 DOTA-NOC PET/CT for defining the receptor status of these patients in July 2004 and have performed over 800 receptor PET/CT studies before and after therapy up to now. Of all known peptides, the somatostatin analogue DOTA-NOC shows in vitro the highest affinity to somatostatin receptors (sstr) 3 and 5. Using PET/CT and the Ga-68 labeled octapeptide DOTA-NOC, standardized uptake values (SUV) of the tumor as well as the molecular tumor volume (MTV) can be calculated. The molecular tumor index (MTI) is defined as the product of SUV x MTV. SUV and MTI can be used to measure tumor response after peptide receptor therapy. Using a prospective database, we are now able to calculate the relation between tumor doses achieved during PRTT (using the Lu-177 or Y-90 labeled peptides) and the relation to the molecular tumor index (MTI) as obtained by receptor PET/CT before the treatment. In future, we are planning to perform full pre-therapeutic organ and tumor dosimetry using receptor PET/CT and longer lived positron emitters (e.g. Sc-44 Y-86 or Cu-64) coupled to the peptides used for therapy.