Use of 18F FDG PET and the short temporal response of Hodgkin's disease to RIT

Improved Quantification of 18F-FDG PET during 131I-Rituximab Therapy on Mouse Lymphoma Models after 131I Prompt Emission Correction

¹⁸F-FDG Positron Emission Tomography (PET) is used to monitor tumor response to ¹³¹I-therapy, but is confounded by prompt emissions (284, 364, 637, and 723 keV) from ¹³¹I, particularly in animal PET imaging. We propose a method for correcting this emission in ¹⁸F-FDG PET. The ¹³¹I prompt emission effect was assessed within various energy windows and various activities. We applied a single gamma correction method to a phantom and in vivo mouse model. The ¹³¹I prompt emission fraction was 12% when 300 µCi of ¹³¹I and 100 µCi of FDG were administered, and increased exponentially with escalating ¹³¹I activity for all energy windows. The difference in spill-over ratio was reduced to <5% after ¹³¹I prompt emission correction. In the mouse model, the standard uptake value (SUV) did not differ significantly between FDG PET only (gold standard) and FDG PET after ¹³¹I prompt emission-correction, whereas it was overestimated by 38% before correction. Contrast was improved by 18% after ¹³¹I prompt emission correction. We first found that count contamination on ¹⁸F-FDG follow-up scans due to ¹³¹I spilled-over count after ¹³¹I rituximab tumor targeted therapy. Our developed ¹³¹I prompt emission-correction method increased accuracy during measurement of standard uptake values on ¹⁸F-FDG PET.