Urethra contouring on computed tomography urethrogram versus magnetic resonance imaging for stereotactic body radiotherapy in prostate cancer.

Accurate urethra contouring is critical in prostate SBRT. We compared urethra contouring on CT-urethrogram and T2-weighted MRI. The dice similarity coefficient, Jaccard index, Hausdorff distance and mean distance to agreement were evaluated. All four metrics indicate better agreement and less variability in urethra contouring on CT-urethrogram, compared to T2-weighted MRI.