Clinical Use Of Dose Response Curves

Dose Response Curves

Dose response curves can be generated for tumour control or normal tissue complications. If compared, the ratio between the two curves at a particular dose is the therapeutic index.
If the curves can be shifted (eg. by drugs, oxygenation etc) then the therapeutic index is altered, possibly providing a beneficial effect.

Chemotherapy and Dose Response Curves

Chemotherapy agents which sensitise cells to radiation will usually shift the tumour control and normal tissue complication curves to the left - ie: a greater effect for a similar dose. If chemotherapy widens the gap between tumour control and normal tissue complications for a particular dose, then the therapeutic index will be improved and chemotherapy may be beneficial.
This explains why, for some treatments, a reduced fraction size or dose is used when concurrent treatment is used instead of radiation alone.