A simple dose gradient measurement tool to complement the conformity index

Defines the gradient index (GI) as the ratio of the volume of half the prescription isodose to the volume of the prescription isodose — for a plan normalized to the 50% isodose line, the 25% isodose volume over the 50% isodose volume. The authors use it to compare plans of equal conformity, to explore prescription isodoses and to compare treatment modalities. Definition read in the abstract (Europe PMC); citation checked against Crossref.

The origin of the gradient index: the half-prescription isodose volume divided by the prescription isodose volume, used to compare plans of similar conformity.