Measured human dosimetry of 68Ga-DOTA-UBI 29-41, a potential tracer for imaging bacterial infection processes

Objectives Ubiquicidin 29-41 (UBI 29-41) is a synthetic antimicrobial peptide fragment reported to be highly specific to accumulate at sites of bacterial infection. The aim of this research was to evaluate the biodistribution and radiation dosimetry of ⁶⁸Ga-DOTA-UBI 29-41 based on whole body (WB) PET imaging in healthy human subjects.

Methods Four healthy volunteers (2 women, 2 men, 28±2 y, 25-27 y, 74.5±22.0 kg, 52-97 kg) were included. Three WB (vertex to mid-thigh) PET/CT scans were acquired on a Siemens Biograph 64 PET/CT scanner at 3 time points (30, 60 and 120 min) after intravenous injection of the tracer (199±22 MBq). Subjects did not void the bladder until the entire series of images was completed. Low-dose CT scans without contrast were used for anatomic localization and attenuation correction. PET images were reconstructed using OSEM-2D algorithm applying appropriate corrections for decay, attenuation, scatter and random coincidences, and normalization. Images were analyzed using OsiriX MD software by drawing volumes of interest in source-organs to determine radiotracer uptake. OLINDA/EXAM software was used to estimate human radiation doses using the reference adult model.

Results /b> PET images revealed a biodistribution of ⁶⁸Ga-DOTA-UBI 29-41 with rapid clearance from circulation through urinary excretion (kidneys and urinary bladder). The critical organ was the urinary bladder wall with absorbed doses (women and men, respectively) of 233±12 and 185±11 µGy/MBq, using the 1-h voiding-bladder model, followed by kidneys with absorbed doses of 81±51 and 34.1±1.1 µGy/MBq. The mean effective dose was estimated as 24.1±0.5 µSv/MBq for female and 18.7±0.5 µSv/MBq for male.

Conclusions ⁶⁸Ga-DOTA-UBI 29-41 is rapidly cleared from the body by urinary excretion. The mean effective dose (all subjects, men and women) for a typical injected activity of 185 MBq is on the order of 4 mSv, which is similar to other ⁶⁸Ga-labeled radiopharmaceuticals, but lower compared to other radiopharmaceuticals currently used for the diagnosis of infection. The dose to the urinary bladder wall can be reduced with frequent bladder voiding. Research Support: This research was supported by UNAM-DGAPA-PAPIIT IT201115.