Prostate cancer: retrograde urethrography to improve treatment planning for radiation therapy.

Thirty men with clinical stage A or B prostate cancer underwent retrograde urethrography at the time of simulation. The inferior edge of the prostate apex was visualized as an abrupt narrowing of the column of contrast material at the urogenital diaphragm. The distance between the line connecting the lower poles of the ischial tuberosities and the site of abrupt narrowing of the column of contrast material (prostate apex) ranged from 0.2 cm to 2.9 cm (median, 1.5 cm). In eight of the 30 (27%) cases, this distance was less than 1.0 cm. In these patients, it would have been inappropriate to place the lower field edge at the bottom of the ischial tuberosities because this would have resulted in an insufficient margin (less than 1.0 cm) below the prostate apex. The authors quantify the percentage of patients who would not be adequately treated if the ischial tuberosities were used as the lower border of the treatment fields. The information obtained at retrograde urethrography can be used to place the inferior border of the treatment fields properly, at least 1.0 cm below the prostate apex.