A monoclonal antibody labeled with the positron-emitting radionuclide 76Br (T 1/2 16.2h) has previously been shown useful for positron emission tomography (PET) imaging of experimental tumors. Our aim in the present study was to investigate the effects of the complex decay scheme of this radionuclide on normal organ dosimetry and PET image quality. Three mini- pigs were injected intravenously with 46-75 MBq of the 76Br-labeled anti- CEA antibody 38S1, and the whole-body kinetics followed by PET imaging for 19 h. From PET data, absorbed doses in human organs were estimated using the MIRDOSE 3.0 software. The highest 76Br concentrations were found in lungs, after a correction for the air volume in this organ. The lungs received the highest absorbed dose (mGy/MBq, mean±maximum error), 0.84±0.16, followed by liver, 0.74±0.28, and small intestine, 0.55±0,05, while the effective dose equivalent was 0.41±0.03 mSv/MBq. The PET imaging properties of 76Br in a two-dimensional 2D PET camera, including central area resolution and scattering effects, were investigated in phantoms and compared to those of 18F. In a 0.97 g/cm3 material, approximating soft tissue density, the FMHW ('full width at half-maximum') value of the point spread function was 7.7±0.2mm for 76Br and 6.0±0.1 mm for 18F. In conclusion, radioimmuno PET using 76Br-labeled antibodies resulted in a fairly even distribution of the radiation dose, where the highest absorbed organ doses were only about two to three times higher than the mean absorbed body dose. The high energy β+ spectrum in the 76Br decay had only minor effects on the resolution, but may decrease the quantification accuracy, especially in organs with a lower density such as a lung.
- Monoclonal antibodies
- Positron emission tomography
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging