A new, accurate and conventional five-point method for quantitative evaluation of ascites using plain computed tomography in cancer patients

Background: To assess the exact response of the malignant ascites to the treatment, the objective measurement of the volume of ascites is essential. We have developed a simple method to measure the volume of ascites by using standard abdomino-pelvic computed tomography (CT). The aim of the study is to validate the accuracy of the measurements by comparing them with the standard volume calculation by using 3D-CT. Methods: Twelve consecutive patients with cancer who had measurable ascites underwent 15 helical CT examinations. On conventional CT images, the thickness of ascites in centimeters was measured in three planes such as the bilateral subphrenic space (A and B), the bilateral paracolic space (C and D) and the pre-bladder space (E), and the average thickness: (A + B + C + D + E)/5 was then multiplied by the area of standard abdominal cavity in the anterior projection, that was assumed to be 1000 cm(2), to yield the volume of ascites: (A + B + C + D + E) x 200 (ml). The volume of ascites was compared with the exact volume, that was obtained from 3D-CT with the volume rendering method. Results: The volume of ascites measured by the present method and the volume rendering method ranged from 140 to 4040 ml and from 86 to 4279 ml, respectively. The correlation was statistically significant with a correlation coefficient of 0.956 (P < 0.01) using the Spearman's rank correlation. In 13 examinations with the exact volume >= 300 mi, the average ratio of the absolute difference in the volume was 12.9 +/- 13.9% as compared with 62.8 and 162.0% in two examinations with the exact volume < 300 ml. Conclusion: The preliminary study indicated that the present five-point method using a conventional CT was accurate in patients with the volume of ascites >= 300 mi. Because this procedure is simple and easy to perform, it should be feasible in many hospitals for the follow-up of ascites after treatment.