Effects of urethrography on prostate position: Considerations for radiotherapy treatment planning of prostate carcinoma

Purpose: Retrograde urethrography is commonly used to define the prostate a pex at simulation, This study evaluated the hypothesis that urethrography c auses prostate displacement, resulting in an error in treatment planning, Methods and Materials: Forty-five patients with carcinoma of the prostate w ere evaluated. Gold seeds were placed in the apex, posterior wall, and base of the gland. In the first 20 patients, the position of the seed-defined a pex was compared at simulation (with urethrogram) and on day 1 of treatment (without urethrogram). In the second cohort of 25 patients, the effects of urethrography on prostate position were evaluated directly at simulation b y comparing the position of apex pre- and post-urethrography, An analysis w as performed to estimate the possible impact of urethrogram-induced prostat e motion on target coverage. Results: The mean superior displacement in the first and second cohort was 5.2 mm and 6.8 mm, respectively (combined mean shift 6.1 mm), With a IO-mm field margin below the tip of the urethrogram cone, 56% of patients in this study would have inadequate planning target volume (PTV) coverage. Conclusion: Retrograde urethrography causes a significant superior shift of the prostate. Strict reliance on urethrography in determining the inferior field margin could result in inadequate treatment. (C) 2000 Elsevier Scien ce Inc.