Computed Metric Library

IN THIS ARTICLE

This article enumerates the custom metrics available in ProKnow and covers some frequently asked questions about these metrics.

Metric Library

The following metrics are available in ProKnow as computed metrics. You can also define custom metrics to track other factors that are important to you.

  • Dose (Gy) covering specified volume (%) of ROI
  • Dose (Gy) covering specified volume (cc) of ROI
  • Dose (Gy) covering whole ROI minus specified volume (cc)
  • Volume (%) of ROI covered by specified dose (Gy)
  • Volume (cc) of ROI covered by specified dose (Gy)
  • Volume (%) of ROI covered by a specified dose range (Gy)
  • Volume (cc) of ROI covered by a specified dose range (Gy)
  • Total ROI volume (cc)
  • Min ROI dose (Gy)
  • Mean ROI dose (Gy)
  • Max ROI dose (Gy)
  • Integral ROI dose (Gy · cc)
  • Global max dose (Gy)
    Max dose value over the whole dose grid
  • Structure(s) containing global max point
    Allows assurance that global max point is in target(s)
  • Serial slice evaluation
    Determines if any axial slices of ROI have min dose > threshold dose
  • Conformation Number
    (Specified ROI volume-at-dose)2/(vol ROI · total irradiated volume-at-dose)
  • Conformality Index
    (Volume receiving specified dose)/(volume of specified ROI)
  • Homogeneity Index
    (Specified ROI D01% – D99%)/(prescription dose)
  • Inhomogeneity Index
    (Max ROI dose – min ROI dose)/(mean ROI dose)
  • Volume of Regret
    Volume (cc) receiving specified dose but outside specified ROI
  • Irradiated Volume
    Total volume (cc) receiving specified dose over whole grid
  • Cumulative meterset
    (MU or min) over all treatment beams

Frequently Asked Questions

Q: Why does my treatment planning system report different metric values from ProKnow?

Some treatment planning systems calculate DVHs differently from ProKnow. Read more about these differences in How ProKnow Calculates DVH Values.

Q: What is the "Conformation Number" metric?

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)

References

Feuvret et al. “Conformity Index: A Review,” Int. J. Radiation Oncology Biol. Phys 2006; 64(2).

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