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Feasibility study of intraoperative gamma probes for determining 177Lu-octreotate activity concentration in vivo

Conference contribution
Authors Ingun Ståhl
Viktor Sandblom
Roger Olofsson Bagge
Eva Forssell-Aronsson
Published in SWE-RAYS (Swedish Radiation Research Association for Young Scientists) 3e årliga workshop, Malmö.
Publication year 2014
Published at Institute of Clinical Sciences, Department of Radiation Physics
Institute of Clinical Sciences, Department of Surgery
Language en
Subject categories Cancer and Oncology, Radiological physics


INTRODUCTION 177Lu-octreotate is a good alternative for treatment of neuroendocrine tumors, with primarily kidneys as limiting organs. The development of a new treatment method using 177Lu-octreotate for liver metastases is under progress at our institute. This treatment method requires accurate activity concentrations of 177Lu-octreotate in tumor and normal tissues in vivo during surgery. Intraoperative gamma probes are mainly used for radio-guided surgery, where diagnostic radiopharmaceuticals including e.g. 99mTc or 111In are frequently used. The aim of this study was to investigate the possibility of using an intraoperative gamma probe for determining 177Lu-octreotate activity concentration in vivo. METHODS The performance of two intraoperative gamma probes was evaluated by determining the range for linear response and the spatial resolution (FWHM) at different depths using different sources containing 177Lu. To illustrate clinical conditions and further explore the ability of the gamma probes to distinguish tumor from normal tissues, measurements using various phantoms were performed. Tumor phantoms, made of agarose gel spheres (5-20 mm diameter) contained a high activity concentration of 177Lu, and were placed in a gel background containing a lower activity concentration of 177Lu, simulating tumors in a normal tissue. RESULTS A linear response (within ±10 %) was found for activities in the range of 1-30 MBq. The spatial resolution (FWHM) increased with depth (0 to 80 mm) from about 10 to 70 mm. The tumor phantom measurements showed high ratios between count rates measured over the gel spheres and the background gel, which indicates a good ability to distinguish between tumor and normal tissue. CONCLUSION The results in the present study imply that an intraoperative gamma probe could be used for measurements of activity concentration of 177Lu-octreotate in tissues in vivo.

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