Prostate volume measurement by transrectal ultrasound and computed tomography before and after permanent prostate brachytherapy

Abstract

Purpose To quantify prostate volume (pvol) changes with transrectal ultrasound (TRUS) immediately after permanent prostate brachytherapy (PPB) and to correlate these changes with postimplant computed tomography (CT) volumetrics. To provide data relevant to evaluating the potential of TRUS-based image fusion for intraoperative dosimetry. Methods and materials Between July 2000 and January 2003, 177 patients underwent 125I PPB monotherapy at our institution, and 165 patients provided research authorization. A total of 136 patients (82%) completed 4 imaging studies: planning TRUS, intraoperative pre- and postimplant TRUS, and CT. Results Mean planning TRUS pvol was 38.7 ± 11.7 cc standard deviation (SD), 95% confidence interval (CI) (36.7, 40.7). Mean intraoperative TRUS pvol preimplant was 37.1 ± 11.7 cc SD, 95% CI (35.1, 39.0), and postimplant was 44.5 ± 15.1 cc SD, 95% CI (42.0, 47.1). The mean ratio of postimplant:preimplant intraoperative TRUS pvols was 1.2 ± 0.2 SD, 95% CI (1.18, 1.24), and the difference in mean values was 7.5 cc ( p < 0.0001). CT performed within 1 day revealed a mean pvol of 47.9 ± 15.7 cc SD, 95% CI (45.2, 50.5). The mean volumetric ratio of CT to postimplant TRUS pvol was 1.13 ± 0.36, 95% CI (1.07–1.19). Conclusions Whereas mean preimplant step-section TRUS pvol measurements are similar, postimplant TRUS and CT measurements have greater variability that depend on initial pvol. CT-based pvol measurements determined a mean of 10.6 hours after implant were more likely to be identical to those of immediate postimplant TRUS in prostates >33 cc. These data are relevant for establishing accuracy in image-fusion based approaches being investigated for real-time intraoperative PPB dosimetry.