Variation in Clinical Target Volumes for Post-prostatectomy Patients and Effect on Normal Tissue Complication Probability

Background: Modern radiotherapy requires accurate contouring which may suffer in the postsurgical setting. We estimated post-prostatectomy interand intra-rater contouring reliability and assessed the effect on bladder and rectal normal tissue complication probability (NTCP). Methods: Four physicians each contoured two different treatment plans, separated by at least seven days, on 15 patients receiving post-prostatectomy four-field 3D-conformal radiotherapy. The Pinnacle 8.0 system determined CTV volume, shape, and center-of-volume coordinates. Interand intra-rater reliability was estimated using Gilder's method. NTCP were estimated using parameters TD50=8190 cGy, n=0.23, m=0.19 for rectum and TD50=8000 cGy, n=0.5, m=0.11 for bladder. Results: Reliability estimates for center-of-volume were ≥0.993. Inter-rater reliability was ≤0.290 and intra-rater reliability between 0.375-0.729 for shape and volume. Inter-rater reliability estimates of NTCP were 0.398 for bladder and 0.0936 for rectum with highest interrater variation 4% and 8%, respectively. Intra-rater reliability NTCP estimates were 0.650 for bladder and 0.186 for rectum, with highest intra-rater NTCP variation 3% and 7%, respectively. Conclusions: Center-of-volume coordinates showed excellent agreement while volume and shape showed poor inter-rater, but moderate intra-rater, agreement. NTCP estimates showed generally poor agreement, but these differences were clinically significant only for rectum (not bladder), based on an a priori definition. Categories: Radiation Oncology, Urology, Oncology 1 2 3 4 5 6 7 8 9 10 11 12 Open Access Original Article DOI: 10.7759/cureus.220 How to cite this article Klein J, Walter A, Wong E, et al. (October 21, 2014) Variation in Clinical Target Volumes for Postprostatectomy Patients and Effect on Normal Tissue Complication Probability. Cureus 6(10): e220. DOI 10.7759/cureus.220