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The effect of delineation method and observer variability on bladder dose-volume histograms for prostate intensity
Tara Rosewall1, Andrew J Bayley, Peter Chung
1Princess Margaret Hospital and Department of Radiation Oncology, University of Toronto, Canada. Tara.Rosewall@rmp.uhn.on.ca
Purpose:
To quantify the effect of delineation method on bladder DVH, observer variability (OV) and contouring time for prostate IMRT plans.
Materials And Methods:
Planning CT scans and IMRT plans of 30 prostate cancer patients were anonymized. For 20 patients, 1 observer delineated the bladder using 9 methods. The effect of delineation method on the DVH curve, discrete dose levels and delineation time was quantified. For the 10 remaining CTs, 6 observers delineated bladder wall using 4 methods. Observer-based volume variation and intraclass correlation coefficient (ICC) were used to describe the dosimetric effects of OV.
Results:
Manual delineation of the bladder wall (BW_m) was significantly slower than any other method (mean: 20 min vs. ≤ 13 min) and the dosimetric effect of OV was significantly larger (V70 Gy ICC: 0.78 vs. 0.98). Only volumes created using a 2.5mm contraction from the outer surface, and a method providing a consistent wall volume, showed no notable dosimetric differences from BW_m in both absolute and relative volume.
Conclusions:
Automatic contractions from the outer surface provide quicker, more reproducible and reasonably accurate substitutes for BW_m. The widespread use of automatic contractions to create a bladder wall volume would assist in the consistent application of IMRT dose constraints and the interpretation of reported dose.
