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Dosimetric consequences of using a surrogate urethra to estimate urethral dose after brachytherapy for prostate
Hoon K Lee1, Warren D D'Souza, Jose-Miguel J Yamal
1Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston 77030, USA.
Purpose:
To assess the accuracy and dosimetric consequences of defining a surrogate urethra at the geometric center of the prostate in postimplant CT scans.
Methods And Materials:
Eighty postimplant CT scans were obtained with a Foley catheter in place at Day 0 and at 1 month for 40 patients who had undergone (125)I prostate brachytherapy. The percentage of urethral volume receiving at least 275% of the prescribed dose (uV(275)), uV(250), uV(200), uV(150), maximal dose received by 90% of urethral volume (uD(90)), uD(70), uD(30), and uD(1) were measured for the Foley catheter and surrogate urethra. The distance between the Foley catheter and surrogate urethra was measured at the base, middle, and apex of the prostate.
Results:
A statistically significant difference was found in all the above-listed dosimetric parameters between the Foley catheter and surrogate urethra at Day 0 (p
Conclusion:
Using a surrogate urethra at the geometric center of the prostate may significantly overestimate the urethral dose at Day 0 and certain dosimetric parameters at 1 month. An alternative position for a surrogate urethra accounting for the difference in the location of the Foley catheter near the base of the prostate at Day 0 and 1 month could be considered in future studies.
