R8.6: Tumour Control Probability Curves

Tumour control probability curves are also called dose response curves.

## Generation of tumour control probability curves

A tumour control probability curve is a plot of cure rate versus dose. Curves are typically sigmoid in shape, with minimal chance of cure at low doses, a rapid rise in cure rate once a particular dose is achieved, which slows as dose increases further.

Tumour control probability curves may be determined using Poisson statistics, which are based on the number of lethal 'hits' per cell (see Random nature of cell kill topic).

## Normal Tissue Complication curves

The rate of normal tissue complications follows a similar curve to tumour control, ideally shifted to the right (less complications than tumour control). The ratio of tumour control to normal tissue complications is the

**therapeutic index**or

**therapeutic ratio**. In the example above, there is a therapeutic index of about 1.8 (65% chance of tumour control, 35% chance of normal tissue side effects).

Clinical use of dose response curves