  For efficient application of protons and light ions in radiotherapy, detailed
knowledge and realistic models of the corresponding radiobiological mechanism
are necessary. Basic characteristics of this mechanism have been represented
within a probabilistic two-stage model. The processes that occur immediately
after the traversals of individual particles and the response of cell to the
total damage formed by all the particles have been distinguished. The model
involves a probabilistic description of DNA damage formation and repair
processes, too.
