The Limitation of the Linear-Quadratic Model at Low Doses per Fraction
The Linear-Quadratic (LQ) equation is used widely to model and predict the increase in total dose with decreasing dose per fraction needed for an isoeffective response to radiotherapy in normal tissues and tumours (reviewed by Joiner 1989). It is thought that this relationship reflects the gradual decrease in radiation effectiveness (“per unit dose”) with lowered doses due to these doses being further and further back “on the shoulder” of an underlying survival curve for the cells at risk in tissues. A considerable amount of work has been devoted to defining the operational limits of this model in a range of normal tissues and tumours during the last 10 years although these studies have been largely done on animal models for ethical reasons. What information there is on human dose-fractionation characteristics and repair kinetics does indicate that the animal systems predict the apparent situation in man reasonably accurately (Thames et al. 1990).
KeywordsUnit Dose Neutron Dose Incomplete Repair Clinical Radiosensitivity Isoeffect Dose
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