Physics Bucharest 2017

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 OV/EV = 1 Perfect conformity

Conformity index (CI)

= 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

OV = GTV PET

꒢ GTV CT

Intersection Conjunction

GTV CT

EV = GTV PET

꒡ GTV CT