An interobserver study of prostatic fossa clinical target volume delineation in clinical practice: are regions of recurrence adequately targeted?

To study interphysician variability of delineation of the prostatic fossa clinical target volume (pfCTV) to be irradiated in patients with residual or recurrent microscopic prostate cancer following radical prostatectomy and to estimate the risk for a geographical miss.

Thirty-eight pfCTV were delineated on postradical prostatectomy computerized tomography scans of 8 patients by 5 observers. To estimate the risk of a geographical miss, a high risk volume (HRV) was defined and the percentage of "missed" HRV was calculated for each pfCTV.

Interphysician variability was considerable with a mean pfCTV of 39.09 cm (range, 11.8-72.5 cm). At least 25% of the HRV at the bladder neck/anastomosis and the retro-vesical space was excluded in 11 pfCTVs. The mean "missed" HRV was 27.5% (range, 2.3%-78.7%). A pfCTV of less than 30 cm was associated with a geographical miss in 66% of cases versus 17.2% for pfCTV of 30 cm or more (P = 0.006). Observer identity was significantly associated with excluded HRV (P = 0.03).

pfCTV delineation is subject to considerable interobserver variability associated with a significant risk of inadequate targeting of the anastomosis/bladder neck region and the retrovesical space. The failure to recognize regions at high risk for harboring microscopic disease may be due to a lack of familiarity with tissue redistribution following radical surgery, and a lack of literature-based guidelines for pfCTV delineation. A strategy to improve pfCTV delineation is proposed.