Abstract: Transrectal ultrasound is used for accurate planning and targeting of placement of radioactive seeds by needles into the prostate in transperineal prostate brachytherapy. The pubic arch formed by the union of the pelvic bones is a potential barrier to passage of the needles containing the radioactive seeds. An initial image of the pubic arch is also provided by transrectal ultrasound, in addition to a transverse cross-sectional image of the prostate. The initial image of the pubic arch is processed using a technique to selectively enhance the contrast of the linear features of the edge of the ultrasound image. The enhanced image is then thresholded via the use of a percentile thresholding technique and then a curve modeling the shape of the pubic arch is fitted against the thresholded, enhanced image to produce a processed image of the pubic arch. This is then overlaid with the image of the prostate and a determination made as to pubic arch interference.