Figure 2.

The relationship between total dose and number of fractions which result in the same low risk (iso-effect) of spinal cord paralysis, obtained using the LQ model with αβ = 2 Gy. Thegrey points correspond to safe treatment schedules, all of which are below theiso-effect curve. The red points are the doses often used to treat squamous cell cancers and which exceed the iso-effect curve. Clinical radiotherapy may utilise the grey dose-fractionation points to palliate cancer close to the spinal cord, but when the red point curative doses are given, great care is taken to ensure that the spinal cord doses are either on or below the curve (reproduced with permission from Jones).