Fig. 2.

a, Sagittal cone beam computed tomography image with associated transperineal ultrasound image depicting prostate guidance positioning volume contour (blue) and fiducial marker identified visually (green arrow). b, c, Guidance positioning volume features visible on transperineal ultrasound images but not cone beam computed tomography images. High-intensity (white) ultrasound features seen in the central region of the prostate likely are calcifications. Ultrasound features are also observed near the urethra and bladder-prostate interface. (A color version of this figure is available at https://doi.org/10.1016/j.ijrobp.2018.04.008.)