Comparability of CT-based and TRUS-based prostate volumes.

PURPOSE To compare the prostate volumes defined by transrectal ultrasound (TRUS) versus computed tomographic (CT) scans used for brachytherapy planning. METHODS AND MATERIALS Ten unselected patients underwent evaluation for prostate brachytherapy with TRUS and CT imaging. Axial prostate contours were obtained at 5-mm intervals in both studies. The CT images were photographed, scanned into a commercial software program, and reprinted from a laser printer at 600 dots per inch to provide individual images that were interpreted independently by the three physician authors (BK, KW, and JB). An effort was made to exclude pelvic floor muscles from the defined prostate contour. Volumes were calculated in cubic centimeters. The prostate volume and maximum dimension in each plane were compared for each imaging modality. RESULTS The CT-based prostate volumes ranged from 31.1 cc to 48.1 cc. The TRUS-based volumes ranged from 26.6 cc to 46.4 cc. There was close agreement between imaging modalities (r = 0.9). The anterior-posterior, lateral, and craniocaudal prostatic dimensions were similar between modalities. To test for consistency between observers, the CT volumes were drawn independently by KB, KW, and JB. The prostatic measurements were consistent in all dimensions between observers. CONCLUSION CT scan volumes and measurements correlate well with those obtained by TRUS, and are appropriate for pre- or postimplant dosimetry.