Positron emission tomography and radioimmunotargeting - Aspects of quantification and dosimetry

Positron emission tomography (PET) is a medical imaging tool with high reso lution and good quantitative properties, which makes it suitable for in viv o quantification of radioimmunotargeting agents. Most radionuclides used in radioimmunotherapy have positron-emitting analogues, which can be used for PET imaging, and this opens the possibility of performing dosimetry with P ET. These isotopes, however, often emit gamma radiation and high-energy pos itrons in their decay, influencing the imaging properties of PET. Spatial r esolution, reconstructed background and line source recovery for a number o f non-pure positron emitters were investigated and compared with the imagin g properties of F-18. PET imaging properties did not decade severely for th ese non-pure positron emitters, but caution has to be applied when doing qu antitative measurements. To assess the possibility of conducting PET studie s during therapy, by combining, for example, a small amount of I-124 With I -131, the influence of the presence of large amounts of gamma radiation on PET count rate characteristics was studied. The results of these studies we re related to the necessary amounts of radioactivity needed for treatment o f post-operative remains of glioma. The results indicate that the count rat e capabilities of 2D PET permit PET studies for dose evaluation during radi oimmunotherapy.