Patient dosimetry of intravenously administered Tc-99m-annexin V

Annexin V labeled with Tc-99m is evaluated as a potential in vivo marker fo r tissue with increased apoptosis, Promising results in patients have been obtained with Tc-99m-(n-1-imino-4-mercaptobutyl)-annexin V (Tc-99m-i-AnxV). Because information on biodistribution and radiation burden is desired for the application of any radiopharmaceutical, a dosimetric study of Tc-99m-i -AnxV was undertaken. Methods: Eight persons with normal kidney and liver f unctions were included in this study: six patients with myocardial infarcti on, one with Crohn's disease, and one healthy volunteer. Approximately 600 MBq (99m)-i-AnxV were injected intravenously immediately before a dynamic s tudy with a dual-head gamma camera in conjugate view mode. In the next 24 h , two to four whole-body scans were acquired. Patient thickness was determi ned from a transmission scan with a Co-57 flood source. Organ uptake was es timated after correction for background. attenuation, and scatter, using a depth-independent buildup factor and an organ-size-dependent attenuation co rrection. Residence times were calculated from the dynamic and whole-body s tudies and used as input for the MIRDOSE 3.1 program to obtain organ-absorb ed doses and effective dose. Results: Activity strongly accumulated in the kidneys (21% +/- 6% of the injected dose at 4 h postinjection) and the live r (12.8% +/- 2.2%). Uptake in the target tissues (myocardium or colon) was limited and negligible from a dosimetric point of view. The biologic half-l ife of activity registered over the total body was 62 +/- 13 h, Of the excr eted activity, similar to 75% went to the urine and 25% to the feces. The a bsorbed dose for the more strongly exposed organs was (in mu Gy/MBq): kidne ys, 93 +/- 24; spleen, 22 +/- 6; liver, 17 +/- 2; testes, 15 +/- 3; thyroid , 10 +/- 6; urinary bladder wall, 7.5 +/- 2.6; and red bone marrow, 5.5 +/- 0.8. The effective dose was 9.7 +/- 1.0 mu Sv/MBq, corresponding to a tota l effective dose of 5.8 +/- 0.6 mSv for a nominally injected activity of 60 0 MBq. Conclusion: Tc-99m-i-AnxV strongly accumulates in the kidneys and to a lesser degree in the liver. The associated effective dose per MBq is in the midrange of values found for routine Tc-99m-labeled compounds. From a d osimetric point of view Tc-99m-i-AnxV is therefore well suited for the stud y of apoptosis in patients.