Abstract
In in vitro irradiation experiments using a broad, non-targeting beam, charged particles pass through the sample randomly, some pass through the cell and others not. In this case, absorbed dose in Gy unit is determined as the quotient of the energy absorbed in the sample to the sample mass, neglecting the information on the site of energy deposition events. Composition of the sample, cells and medium, is averaged all over the dish. In the microbeam experiments, however, the track of charged particles are localized, for example, in the cell nucleus. How can we determine the dose and compare the results obtained in microbeam experiments with those in broad beam experiments? In order to calculate the absorbed dose, we need to define the sample or the target that absorbed the radiation energy. One of the candidates of the target might be the cell itself, since the cell is an independent entity in living organisms. The reports which indicate that the signals for bystander effects are secreted or leaked out from the cell after processing the signal produced by the track seem to support the above idea. When we use an X-ray microbeam, next question will be raised. If the same number of X-ray photons is delivered with microbeam of different sizes, can we think both cases are the same or not? Some discussions and considerations on these points will be presented.
