ABSTRACT
This chapter highlights the various radiobiological models available to understand the effects of radiation on cells, their principles, and limitations for further development. Radiobiological models (RBMs) are widely used in both conventional and modern radiotherapy for various reasons. In 1944, Strandqvist developed a novel empirical approach to analyze the biological effects of radiation by introducing the dose isoeffect through the isoeffective curve. He adjusted the constant of proportionality k to a treatment scheme and called it nominal standard dose (NSD), which consisted of dose and time parameters with the unit of rad-equivalent therapy (RET). In order to rectify the limitations in the NDS concept, Orton and Ellis introduced the time–dose fractionation (TDF) factor in the NSD and formed a new model called the TDF model. A survival curve of mammalian cells is used to get direct information on their response to radiation.
