Determination of the Urethral Dose in Prostate
Brachytherapy when the Urethra is not Visualized in the Post-Implant CT Scan
F. M. Waterman* and A.P.Dicker
Department of Radiation Oncology
Kimmel Cancer Center, Jefferson Medical College
Thomas Jefferson University
Philadelphia, PA
A urinary catheter is often not utilized when the post-implant CT scan is obtained and
the urethra cannot be visualized to calculate the urethral dose. This study investigates
the feasibility of locating a surrogate urethra at the geometric center of the prostate as
a solution to this problem. Twenty I-125 prostate implants which were scanned utilizing a
urinary catheter were randomly selected. In each implant, the I-125 seeds were implanted
at the periphery of the prostate producing a dose distribution characterized a broad dose
minimum in the central region of the prostate containing the urethra. The urethra was
outlined from the base to the apex of the prostate using the image of the urinary
catheter. In addition, a surrogate urethra was outlined at the geometric center of the
prostate. Dose-volume histograms were compiled and the D10, D25, and D50 doses of the
actual and surrogate urethras were compared. The difference between surrogate urethra dose
and actual urethra dose was 3.3 + 5.5 % (mean + S.D.) at D10, 1.0 +
6.0 % at D25, and 2.3 + 7.1 % at D50. These results show that urethra doses from
D10 to D50 can determined to within + 10% by a surrogate urethra located at the
geometric center of the prostate when the I-125 seeds are peripherally loaded and the
urethra is not visualized in the post-implant CT scan.
Abstracts Submitted to 1999 Annual AAPM Meeting | Medical Physics Home |
