FDG-PET image-based dose distribution in a realistic mouse phantom from Monte Carlo simulations

The purpose of the study was to calculate dynamic internal dose distributions from FDG-PET imaging procedures using a realistic mouse phantom and the Monte Carlo method. A realistic mouse phantom was used for simulations and consisted of a matrix with a voxel size of (400 μm)³ and tissue compositions taken from human counterparts. The GATE software was used to perform all simulations. Dose calculations were performed using discretized, image-based FDG biodistributions from dynamic acquisitions. For each biodistribution - considered constant for some time interval - dose in the phantom was calculated by tracking a sufficient number (10⁸) of primary emitted particles (e+). Dose values were then scaled to take into account radioactive decay and dose integration with time. Dose averages for most organs were between 5 and 15 mGy per MBq of injected activity, with a whole body dose average of 11 mGy/MBq. The heart received about 75 mGy/MBq and for the unvoided bladder scenario, the dose to the bladder wall ranged from 100 to 1000 mGy/MBq, with an average close to 500 mGy/MBq. For a study using 200 μCl of injected tracer, this would translate into 550 and 3600 mGy delivered to the heart and bladder wall, respectively. The biological response and its eventual effect on investigations is unknown although the bladder wall is usually not considered a target tissue. Voiding the bladder at least partially can reduce the total absorbed dose by half.