Variability of manual segmentation of the prostate in axial T2-weighted MRI: A multi-reader study

Purpose: To evaluate the interreader variability in prostate and seminal vesicle (SV) segmentation on T2w MRI. Methods: Six readers segmented the peripheral zone (PZ), transitional zone (TZ) and SV slice-wise on axial T2w prostate MRI examinations of n = 80 patients. Twenty different similarity scores, including dice score (DS), Hausdorff distance (HD) and volumetric similarity coefficient (VS), were computed with the VISCERAL EvaluateSegmentation software for all structures combined and separately for the whole gland (WG = PZ + TZ), TZ and SV. Differences between base, midgland and apex were evaluated with DS slice-wise. Descriptive statistics for similarity scores were computed. Wilcoxon testing to evaluate differences of DS, HD and VS was performed. Results: Overall segmentation variability was good with a mean DS of 0.859 (+/- SD = 0.0542), HD of 36.6 (+/- 34.9 voxels) and VS of 0.926 (+/- 0.065). The WG showed a DS, HD and VS of 0.738 (+/- 0.144), 36.2 (+/- 35.6 vx) and 0.853 (+/- 0.143), respectively. The TZ showed generally lower variability with a DS of 0.738 (+/- 0.144), HD of 24.8 (+/- 16 vx) and VS of 0.908 (+/- 0.126). The lowest variability was found for the SV with DS of 0.884 (+/- 0.0407), HD of 17 (+/- 10.9 vx) and VS of 0.936 (+/- 0.0509). We found a markedly lower DS of the segmentations in the apex (0.85 +/- 0.12) compared to the base (0.87 +/- 0.10, p < 0.01) and the midgland (0.89 +/- 0.10, p < 0.001). Conclusions: We report baseline values for interreader variability of prostate and SV segmentation on T2w MRI. Variability was highest in the apex, lower in the base, and lowest in the midgland.