Biodistribution and radiation dosimetry of the hypoxia tracer 18F-EF5 in oncologic patients

Objectives The primary goal of this Phase I study was to determine the biodistribution and excretion of 18F-EF5 in oncologic patients and to estimate the radiation absorbed dose, metabolism, and safety of this drug.

Methods Sixteen patients (8 men, 8 women) with histologically confirmed malignancy underwent bolus infusion of 18F-EF5 (219 MBq (range 107-366 MBq) at Penn(10) and Turku(6). Over a 4 hour period, four serial PET or PET/CT scans were obtained. To calculate the time-activity curves, residence times, and radiation dosimetry estimates, volumes of interest were drawn over the source organs for each PET scan or on the CT for each PET/CT scan. Serial blood samples were obtained to measure blood clearance. Bladder wall dose was calculated based on urine activity measurements. Safety was assessed by vital signs, ECG, and blood and urine analyses monitoring.

Results The mean urinary bladder radiation absorbed dose was the largest at 0.077 ± 0.043 mSv/MBq (mean ± SD). There were no other mean organ radiation doses exceeding 0.10 mSv/MBq. The average effective dose equivalent of 18F-EF5 was determined to be 0.018mSv/MBq calculated on a 4.8 hour voiding interval. 18F-EF5 was well tolerated in all subjects. No serious adverse events were noted. No clinically significant changes in ECG, vital sign, blood or urine chemistry were found.

Conclusions The average effective dose equivalent of 18F-EF5 was 0.018 mSv/MBq, which is less than that of 18F-FDG (EDE = 0.030 mSv/MBq). The dose to the bladder wall was the highest. As with any radiotracer with primary excretion in the urine, we recommend active hydration and frequent voiding.

Research Support This work was supported by a grant from Varian Medical Systems