Spine SRS

Table of Contents

DVH Conformity Indices


The conformity index indicates how accurately the volume of the dose distribution matches the size and shape of the PTV(s). The software provides the inverse Paddick conformity index (CI) and the gradient index (GI) per target volume.


Inverse Paddick Conformity Index (CI)

The CI describes how well the 100% isodose volume conforms to the target volume. This is computed as the inverse Paddick CI:

  • The first term penalizes normal tissue receiving more than the coverage dose, Dcoverage.

  • The second term penalizes cold spots (dose below the coverage dose) inside the tumor volume.

A perfect theoretical dose distribution would have a CI of “1”.

Gradient Index (GI)

The GI describes the steepness of the dose fall-off from the 100% isodose to the 50% isodose:

A perfect theoretical dose distribution would have a GI of “1”.

Art-No. 60919-40EN

Date of publication: 2019-05-22