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Metrics for volumetric comparisons
Parameter
Formula Interpretation
Ratio PET/CT
GTV
PET
/GTV
CT
Ratio CT/PET
GTV
CT
/GTV
PET
Discrepancy index (DI)
EV/OV = 1 Perfect concordance
= ∞ Complete disagreement
Conformity index (CI)
OV/EV = 1 Perfect conformity
= 0 Complete disconformity
Overlap
Fraction (OF)
or “coverage”
OF
CT
OV /GTV
CT
Proportion of GTV
CT
covered by
GTV
PET
OF
PET
OV /GTV
PET
Proportion of GTV
PET
covered by
GTV
CT
Mismatch
Fraction
(MF)
MF
CT/PET
1 - OF
CT
Volume enclosed by GTV
CT
but
not by GTV
PET
relative to GTV
CT
MF
PET/CT
1 - OF
PET
Volume enclosed by GTV
PET
but
not by GTV
CT
relative to GTV
PET
GTV
PET
GTV
CT
OV = GTV
PET
꒢
GTV
CT
EV = GTV
PET
꒡
GTV
CT
Intersection
Conjunction