Ratios of internal doses deposited in different organs to the whole body when such organ is adopted as source of (18)F-fluorodeoxyglucose, a Monte Carlo Geant4 study on a male medical internal radiation dose phantom

In the present study, the last stable version of Monte Carlo Geant4 code known as Geant4.10.3 has been used for measuring internal dose ratios to the whole body for about 40 organs. This, by performing a Monte Carlo model of (18)F-fluorodeoxyglucose ((18)F-FDG) inside different organs of medical internal radiation dose male phantom, mimics a human male adult of 70 kg. A dedicated Geant4 user code has been developed in the top of one offered by Geant4 Monte Carlo toolkit and so-called human phantom. Several Monte Carlo simulations have been carried out, and in each of them, we have taken up such organ as source of (18)F-FDG with a small amount of radioactivity, evenly distributed across its volume, and we measure ratios of absorbed doses deposited in organs to the whole body. The results have shown that there are radiation dose contributions from surrounding organs and their gravities are so variable; some organs have near-local character; thus, almost all radiations are locally deposited, which generally do not affect surrounding ones mainly including adrenals, thyroid, clavicles, thymus, testes, bladder, pancreas, scapula and upper spine; whereas, it is not the case for many other organs in which radiation doses are deposited outside of their parent volumes. In addition, absorbed doses in some organs that have high-tissue weighting factors, namely colon, lungs, stomach, bladder, thyroid, and liver are seriously affected by radioactivity of surrounding muscle organs, the gravity of such affectation is mainly growth when a patient is identified as having hyperglycemia or undergoing a hard physical activity.