PET/CT biodistribution and dosimetry of [18F]ISO-1 in humans

Objectives The sigma-2 receptor radiotracer, [18F]ISO-1, has shown to be a promising imaging biomarker to assess the proliferative status of tumors in pre-clinical studies. The objective of this work was to characterize the biodistribution and dosimetry of [18F]ISO-1 in humans.

Methods 12 patients with lymphoma, head & neck or breast cancers were studied on a Biograph-40 PET/CT after a single injection of approximately 296 MBq of [18F]ISO-1. Two imaging time points per patient were chosen to sample the [18F]ISO-1 kinetics over a 3.5 hr period. Immediately after the low dose attenuation CT scan, emission images beginning at the pelvis and proceeding to the top of the skull were obtained. The normal biodistribution (extracted from PET/CT images) revealed a rapid uptake in the liver followed by accumulation in the gallbladder and pancreas. Other normal accumulation also was observed in the heart and small intestines. By combining the data from all patients, normal organ time activity curves (TACs) were created and residence times were calculated from the integral of a mono-exponential fit to the TACs accounting for radioactive decay. TACs were created for the liver, lungs, gallbladder, heart, pancreas, kidneys, small intestines (SMI), brain, spleen and urinary bladder.

Results The gallbladder was observed to increase linearly with time at a rate of 0.252% of the injected dose per hour. The average accumulation over the imaging period was observed to be the highest in the gallbladder, pancreas and liver, and the largest residence times were observed to be the liver, gall bladder and SMI. Human radiation dose estimates were computed using OLINDA and the adult male model. The highest doses were 0.09, 0.069 and 0.054 mGy/MBq to the gallbladder, liver, and pancreas, respectively. Under the guideline of 50 mGy for the highest dose to any organ, a maximum amount of 550 MBq can be injected and yield an effective dose of 8.8 mSv.

Conclusions This amount is commensurate with [18F]FDG and therefore allows for safe and efficient imaging of patients.

Research Support Funded by Isotrace Technologies, Inc