ABSTRACT
Organs and tissues are made up from cells having various general or special functions; these cells and their contents are considered the key targets for radiation damage. Low dose ionizing radiation has a nonuniform discontinuous interaction with matter. The related probabilistic nature of energy depositions results in distributions of imparted energy on a cellular and molecular level that are very uneven, due to the low photon density. Absorbed dose is the statistical mean of the distribution of energy imparted in small volumes divided by the mass of the corresponding volume. However, the smaller the average radiation dose to an organ or tissue, the fewer the number of cells that will be hit by an ionizing track. The fluctuations of energy imparted in individual cells and subcellular structures are the subject of microdosimetry.
