How the Software Computes the Conformity Index
The CI and GI are computed by evaluating the dose in the PTV ① plus a normal tissue expansion ring ②. The size is read from the loaded reference plan that was generated in the RT treatment planning software.
The software examines the dose at the border of the normal tissue ring. If the 50% or 100% isodose line is inside the normal tissue ring, the software can compute the respective conformity index ③. If the 50% and/or 100% isodose line is no longer inside the PTV volume and normal tissue ring, the software cannot compute the respective CI/GI ④. If the isodose is exceeded for at least one of the points on the border of the normal tissue ring, the software displays N/A. This typically occurs if the PTVs are located very close to each other. The volume averaged conformity indices will be n/a if the index of at least one of the PTVs is n/a.
If none of the PTV voxels reach the prescription dose, the software displays – – for the conformity indices.