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Feasibility and Potential Impact of Using CT Volume as a Predictor of Specimen Weight in a Subgroup of Patients with Low Risk Wilms Tumors Registered on COG Study AREN03B2
Fernando A. Ferrer, M.D.1, Katherine Herbst, M.Sc.2, Conrad Fernandez, M.D.3, Geetika Khanna, M.D.4, Jeffrey S. Dome, M.D.5, Robert Shamberger, M.D.6, Michael Ritchey, M.D.7, Peter F. Ehrlich, M.D.8.
1Connecticut Children's Medical Center/University of Connecticut Medical School, Hartford/Farmington, CT, USA, 2Connecticut Children's Medical Center, Hartford, CT, USA, 3IWK Health Center, Halifax, NS, Canada, 4Washington University School of Medicine, St. Louis, MO, USA, 5Children's National Medical Center, Washington, DC, USA, 6Children's Hospital of Boston/Harvard Medical School, Boston, MA, USA, 7Mayo Clinic College of Medicine, Phoenix, AZ, USA, 8University of Michigan Medical School, Ann Arbor, MI, USA.

BACKGROUND:
Patients with Wilms tumor stageI, age ≤2 years, tumor< 550 grams may not require therapy beyond nephrectomy. Accurate estimation of specimen weight prior to nephrectomy assists with preoperative planning and informs the decision of whether or not to place a port. The study's aims were to determine if a linear relationship existed between tumor weight and CT estimated volume and to describe the accuracy of a slope-intercept equation in estimating weight.
METHODS:
Tumor weight and port placement were abstracted from 105 age ≤2 patients enrolled in COG AREN03B2. One radiologist estimated tumor size from CT scan. Volume was calculated, linear regression performed, slope-intercept equation calculated, and equation estimated weight determined. Positive predictive value (PPV) was calculated for the equation and the actual outcome (line placement y/n).
RESULTS:
Median volume was 653 cc, and median weight was 409 grams. Fifty-five ports were placed, twenty-nine potentially unnecessarily (tumor wgt <550 grams), and six not placed in patients requiring them (tumor wgt >550). Linear regression demonstrated a strong relationship between volume and weight (R2=0.873,p<.001). The slope-intercept equation for weight (W) based on volume (V) was: W=0.54(V)+58.75. PPV for the equation was 0.8437 vs 0.4727 in the sample population.
CONCLUSIONS:
The relationship between volume and weight produced a viable slope-intercept equation. Precision of the equation was 84% vs 47% in our sample population. If the equation had been used to determine need for port, twenty-four fewer ports may have been placed, while one child would not have had additional surgery for port placement.


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