Use of computed tomography and radiation therapy planning software to develop a novel formula for body surface area calculation in dogs

BACKGROUND: Body surface area (BSA) can reflect metabolic rate that might normalize dosing of chemotherapeutics across widely variable weights within a species. The current BSA formula for dogs lacks height, length, and body condition. HYPOTHESIS: Computed tomography (CT) imaging will allow inclusion of morphometric variables in allometric modeling of BSA in dogs resulting in an improved formula for BSA estimation. ANIMALS: Forty‐eight dogs from 4 institutions with whole‐body CT images. METHODS: Retrospective and prospective case series. Body surface area was contoured using whole‐body CT scans and radiation therapy planning software. Body length and height were determined from CT images and also in 9 dogs by physical measurement. Nonlinear regression was used to model the BSA data sets using allometric equations. Goodness‐of‐fit criteria included average relative deviation, mean standard error, Akaike information criterion, and r(2) (derived from the r‐value generated by regression models). RESULTS: Contoured BSA differed from the current formula by −9% to +19%. Nonlinear regression on untransformed data yielded BSA = 0.0134 × body weight [kg](∧)0.4746 × length (cm)(∧)0.6393 as the best‐fit model. Heteroscedasticity (increasing morphometric variability with increasing BSA) was an important finding. CONCLUSIONS AND CLINICAL IMPORTANCE: Computed tomography‐derived BSA was used to incorporate body length into a novel BSA formula. This formula can be applied prospectively to determine whether it correlates with adverse events attributed to chemotherapy.