Biodistribution and dosimetry of Tc-99m-BTAP-annexin-V in humans

The purpose of this study was to determine the biodistribution and the asso ciated radiation dose of technetium-99m 4,5-bis(thioacetamido)pentanoyl-ann exin-V (Tc-99m-Apomate), a tracer proposed for the study of apoptosis. Eigh t patients (including two females) with normal kidney and liver functions w ere included in the study. An activity of 580 +/- 90 MBq of Tc-99m-Apomate was injected intravenously, immediately followed by a dynamic study of 30 f rames of I min each. At about 1 h, 4 h and 20 h p.i., whole-body scans were acquired. All activity distributions were measured using a dual-head gamma camera. Before injection of activity, a transmission scan with a cobalt-57 flood source had been performed to determine patient attenuation. Blood sa mples were taken every 10 min during the first hour after injection, and at about 4 and 20 h. Urine and faeces were collected during the first 20 h. O rgan uptake was estimated after correction for body background activity, at tenuation and scatter. Residence times were calculated from the dynamic and whole-body studies and used as input in the Mirdose 3.1 program to obtain organ doses and effective dose. It was found that radioactivity strongly ac cumulated in the kidneys and the liver [at 70 min p.i., 28%+/-8% and 20%+/- 4% of the injected dose (ID), respectively]. Uptake in the target tissues ( lymphomas or heart) was negligible from a dosimetric point of view. Extrapo lating data from the first 20 h, one finds that approximately 73% of the ID will be excreted in the urine, and 27% in the faeces. The biological half- life of the activity in the total body was 16 +/-7 h. Some organ doses stan dard deviation (SD) in mu Gy/MBq were: kidneys 63 +/- 22, urinary bladder 2 0 +/-6, spleen 15 +/-3, liver 13 +/-3, upper large intestine 12 +/-6, lower large intestine 8 +/-4, testes 6 +/-2 and red bone marrow 4 +/-0.7. The ef fective dose was 7.6 +/-0.5 mu Sv/MBq, corresponding to a total effective d ose of 4.6 +/-0.3 mSv for a nominal injected activity of 600 MBq. In conclu sion, Tc-99m-Apomate has a high uptake in the kidneys and liver - in fact a factor of 1.3-1.6 higher than that found for the previously studied Tc-99m -(n-1-imino-4-mercaptobutyl)-annexin-V. The biological half-life is shorter , however, but still long compared with the physical half-life of Tc-99m. T he faster appearance of activity in the intestines may preclude imaging of apoptosis in the abdomen. The effective dose is within the lower range of v alues reported for typical Tc-99m compounds.