  It has long been known that radiation biology plays an important role and it
is necessary for radiotherapy treatments. The radiation effects on normal and
malignant tissues after exposure range from a femtosecond to months and years
thereafter [1,2]. Therefore, to optimize treatment, it is crucial to explain
and understand these mechanisms [3-5]. Providing a conceptual basis for
radiotherapy and identifying the mechanisms and processes that underlie the
tumor and normal tissue responses to irradiation can help to explain the
observed phenomena [6]. Examples include understanding hypoxia, reoxygenation,
tumor cell repopulation, or the mechanisms of repair of DNA damage [3,7,8]. The
different biological effects of radiation should be divided into several
phases: physical (interaction between charged particles and tissue atoms),
chemical (the period during which the damaged atoms and molecules react with
other cellular components in rapid chemical reactions), and biological (impact
of the generated lesions on the biological tissue [4]). The following section
describes the models most often used in radiotherapy. These are simplistic
models that actual treatments are based, and that are validated and approved
[9-12].
