ABSTRACT
As soon as relatively accurate dosimetry became available around 1910, it became clear that the biological effect of a given physical dose of ionizing radiation depends on how this dose is distributed over time. For many years, the differential response of tumours and normal tissues to changes in dose-time-fractionation appeared to be the most important means of improving the therapeutic ratio. Mathematical models – often referred to as bioeffect models – were first introduced in the 1920s with the aim of linking the probability of tumour control and normal tissue side effects to the dose of fractionated radiation delivered. The linear-quadratic (LQ) model was introduced around 1980 and this remains the model of choice for bioeffect estimation in radiotherapy.
