Biological effects of high doses of ionizing radiation are reasonably well studied and documented. Nevertheless, there is a clear lack of information and/or evidence concerning biological effects of Low Doses, namely at medical imaging levels, as those characterizing Nuclear Medicine and Radiology typical environments. Our group has being involved in the in vitro study of these low dose radiobiological effects. Preliminary experimental results with 100mGy external gamma irradiation of HepG2 monolayer cells showed a slight increase in the proliferation rate 24h, 48h and 72h post irradiation. These preliminary results also pointed into the presence of some Bystander effects 72h post irradiation, constituting the starting point and motivation for the need of a more accurate analysis , here presented
