There are many conformity indices in our field, some more useful than others.
We often use the “Conformation Number” (CN) metric which was originally described by Van’t Riet et al. The CN does a great job in capturing both the coverage of the target by the reference dose and the shaping of the reference dose outside the target.
The CN is summarized by the equation:
CN = (TVRI * TVRI)/(TV * VRI)
TVRI = Target volume covered by the reference dose (cc), TV = Total target volume (cc), VRI = Volume of the reference dose (cc)
Feuvret et al. “Conformity Index: A Review,” Int. J. Radiation Oncology Biol. Phys 2006; 64(2).