R3.6: Alpha Beta Values

As discussed in the Linear Quadratic Equation topic, the alpha/beta values describe the curvature of a cell survival curve. The alpha/beta ratio is the dose where cell killing due to the linear and quadratic components are equal. In general:

  • The higher the alpha/beta ratio, the more linear the cell survival curve will be
  • The lower the alpha/beta ratio (ie. high beta relative to alpha), the more curved the cell survival curve.

This is important, as for low doses the low alpha/beta tissues are relatively resistant compared with high alpha/beta tissues. This allows for splitting of the effects seen in these tissues if doses in this range are given.

  • Early responding tissues have a high alpha beta ratio
  • Late responding tissues have a low alpha beta ratio
  • Most tumours have a high alpha beta ratio
  • Some tumours (eg. melanoma, sarcoma, prostate) have a low alpha beta ratio