18F-Fluoroerythronitroimidazole radiation dosimetry in cancer studies

18F-Fluoroerythronitromidazole (FETNIM) is a new promising PET tracer for imaging tumor hypoxia. Accurate radiation dosimetry is important for estimating absorbed radiation doses to patients and for calculating the allowable injected dose.

Radiation absorbed doses were estimated from PET scans obtained on cancer patients on the basis of the MIRD procedure. Dynamic acquisition data was obtained from the thorax, abdomen, and head and neck regions. The tracer was injected intravenously and mean injected activity was 366 MBq (range, 288-385 MBq). Arterial blood was continuously assayed over dynamic PET imaging. The bladder wall dose was evaluated from the voided urine activity measurements.

The effective dose to a 70-kg adult was 0.015 or 0.019 mSv/MBq, calculated on 2- or 4-h voiding intervals, respectively. The critical organ proved to be the urinary bladder wall, with a highest absorbed dose of 0.062 or 0.127 mGy/MBq depending on the voiding schedule as described above. Absorbed doses in all other organs were at least 5-fold smaller than the bladder wall doses.

With an injected activity of 370 MBq (18)F-FETNIM, the radiation doses are generally comparable with those of other related radionuclide imaging procedures. Specifically, in comparison with (18)F-fluoromisonidazole, the absorbed doses of (18)F-FETNIM are equal. However, special attention should be given to adequate hydration and voiding to limit the relatively high exposure of the critical organ, bladder wall, to (18)F-FETNIM.