Delineation of the postprostatectomy prostate bed using computed tomography: interobserver variability following the EORTC delineation guidelines

Abstract

Purpose: The present study aims to assess the interobserver agreement of prostate bed delineation after radical prostatectomy using CT alone as proposed by the European Organization for Research and Treatment of Cancer (EORTC) guidelines.

Methods and materials: Six observers delineated the postoperative prostate bed (PB) and the original seminal vesicle position or remnants (SV) of 10 patients according to the EORTC guidelines. Contours were then compared for agreement between observers (the apparent volume overlap and generalized kappa statistics). Standard deviations were also calculated to measure the variability of the position of the outer margins.

Results: The mean volume of 100% agreement (±1 standard deviation, SD) was only 5.0 (±3.3) ml for the PB and 0.9 (±1.5) ml for the SV, whereas the mean union of all contours (±1 SD) was 41.1 (±11.8) ml and 25.3 (±13.4) ml, respectively. The mean overall agreement corrected for chance was moderate for both the PB (mean kappa, 0.49; range, 0.35-0.62) and SV (mean kappa, 0.42; range, 0.22-0.59). The overall SD of the outer margins of the PB ranged from 4.6 to 7.0 mm

Conclusion: The delineation of the postprostatectomy bed using CT shows only a moderate observer agreement when following the EORTC guidelines.