PROSTATE-CANCER - COMPARISON OF RETROGRADE URETHROGRAPHY AND COMPUTED-TOMOGRAPHY IN RADIOTHERAPY PLANNING

Purpose: To prospectively compare the role of retrograde urethrography and high-quality computed tomography during the treatment planning of patients with prostate cancer. Methods and Materials: Forty consecuti ve men with localized prostate cancer underwent planning computed tomo graphy prior to simulation. At the time of simulation we performed ret rograde urethrography and compared the location of the inferior border of the urogenital diaphragm to the location of the ischial tuberositi es and the prostate and base of the penis as seen on the computed tomo graphy scan. Results: Interobserver identification of the prostatic ap ex varied in 70% of the cases. Perhaps due to this variability, attemp ts to place the inferior border of the treatment field in relation to the prostatic apex resulted in an inadequate margin (< 1 cm) beneath t he urogenital diaphragm in 5%. In contrast, placing the inferior borde r at the ischial tuberosities or the base of the penis as seen on comp uted tomography insured an adequate margin for all patients. The dista nce from the urogenital diaphragm to the ischial tuberosities and, thu s, the potential margin beneath the urogenital diaphragm was > 2 cm in 77%, while the distance from the urogenital diaphragm to the base of the penis was greater than or equal to 2 cm in only 43%. Conclusion: T his demonstrates the difficulty in reliably identifying the prostate o n computed tomography. Nevertheless, by identifying the base of the pe nis, planning computed tomography provides adequate information to cov er the target volume, and results in minimal overtreatment of normal s tructures. Urethrograms are not necessary if the computed tomography i s properly used or if the ischial tuberosities are used as a standard inferior border, but they can reduce the length of urethra in the trea tment volume which could potentially reduce complications.