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The Correct Formula to Calculate Volume Overlap

W Lu

W Lu1*, S Tan1,2, (1) University of Maryland School of Medicine, Baltimore, MD, (2) Huazhong University of Science & Technology , Wuhan,

SU-E-J-106 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To describe formulas that are often used incorrectly in calculating overlap between two tumor volumes, and to illustrate the correct formula with simulation and patient data.

Methods: A review of the literature showed that there are various formulas used for calculating volume overlap between two volumes A and B. We demonstrated that formulas using one volume as base (BinA, AinB) led to overestimation or underestimation of the overlap. We illustrated the correct formula of Overlap based on Dice coefficient: 2*Interception/(A+B). We compared the differences with both simulation and patient data.

Results: When A and B had the same volume, there was no differences between all formulas. When the volume of A was larger than the volume of B, BinA overestimated the Overlap while AinB underestimated the Overlap in both simulation and patient data. The formula using max(BinA, AinB) overestimated the Overlap by a factor of almost 2. Overlap based on Dice coefficient agreed well with perceived overlap.

Conclusion: The Dice Coefficient with the sum of two volumes as base should be used to calculate volume overlap.

Funding Support, Disclosures, and Conflict of Interest: National Cancer Institute Grant R21 CA131979

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