The linear-quadratic model in the description of the mechanisms of high-dose radiation therapy
The literature review is dedicated to the main problems of radiobiology which defines the basics of radiation therapy and describes reactions of normal and pathological tissues to radiation and their mechanisms. The implementation of different variants of hypofractionation, and high-dose radiation, including stereotactic radiation therapy and radiosurgery, has shown that the radiobiology of tumors and normal tissues, with these methods applied, does not correspond to traditional concepts specific to classical fractionation, and the traditional linear-quadratic model cannot adequately explain the effects that occur. Attempts are continuously being made in order to modify the linear-quadratic model, however, none of them has so far been able to provide an accurate assessment of cell survival in the high dose range, which is largely due to radiation-induced vascular endothelial damages, activation of immune and nontarget processes. Modified linear-quadratic models need further verification, and they should be used with caution in clinical practice, together with QUANTEC tools. The basic concepts of radiobiology can be reduced to several interrelated models: linear-quadratic, vascular, immune and non-target. There is a need to create a single integrated model that combines the previous ones.