Three-dimensional quantitation of pediatric tumor bulk.

In pediatric oncology, therapeutic decisions are made based on tumor response to chemotherapeutic agents. Sequential measurement of tumor bulk and its percent change on therapy must be accurately assessed. Will 3-dimensional (3-D) volumetric determination improve our ability to assess tumor response to therapy? Forty-five CT scans of pediatric patients with unresectable thoracic or abdominal neoplasia were assessed for tumor bulk by the standard "2-dimensional (2-D)" volume formula (cross-sectional area x length) and by 3-D volumetric analysis. Thirty-two examinations were performed in follow-up, and percent change in tumor size was calculated. The 2-D volume calculation overestimated tumor volume by more than 50% on all but two examinations when the 2-D volume was compared with the 3-D volume. In 28% of follow-up examinations, the 2-D calculation of percent change differed by more than 10% from the 3-D volume. Fifteen percent differed by over 25%. This changed the response category of one patient from "no response" to "partial response". 3-D volumetric analysis, easily performed by a trained technologist, will give more accurate assessment of the actual tumor bulk and its subsequent changes in size in response to therapy.