Is the use of a surrogate urethra an option in prostate high-dose-rate brachytherapy?
OBJECTIVE
To investigate the accuracy and the dosimetric consequences of substituting a surrogate urethra assumed to be at the geometric center of the prostate, in place of the true urethra when using high-dose-rate (HDR) brachytherapy for the treatment of prostate cancer.


METHODS
One hundred prostate cancer patients treated with HDR brachytherapy constituted the study group. A pre-plan was made with the urethra visualized. The true urethra was defined, and a surrogate urethra was placed at the geometric center of the prostate. The distance between the two urethras was measured. The deviation was evaluated at the base, middle, and apex. To evaluate the dosimetric consequences for the true urethra when using a surrogate urethra, two different dose plans were made: one based on the true urethra and one based on the surrogate urethra. The dose-volume histograms for the true urethra were analyzed.


RESULTS
The deviation between the true urethra and the surrogate urethra was greatest at the base of the prostate. A statistically significant difference was seen between the dosimetric parameters for the true and the surrogate urethra when the dose plan was made using the surrogate urethra. In this situation the dose to the true urethra was increased above our defined maximum tolerance limit.


CONCLUSIONS
When using dose plans made according to a surrogate urethra the dose to the true urethra might be too high to be acceptable. If the true urethra is not visualized, severe damage could easily develop in a significant number of patients.
Nilsson
Josef
J
Department of Medical Physics, Radiumhemmet, Karolinska University Hospital, Stockholm, Sweden. josef.nilsson@karolinska.se
Kälkner
Karl Mikael
KM
Berg
Lars
L
Levitt
Seymour
S
Holmberg
Carina
C
Nilsson
Sten
S
Lundell
Marie
M
D000368:Aged; D001187:Artificial Organs; D001918:Brachytherapy / Q000379:methods*; D016009:Chi-Square Distribution; D006801:Humans; D008297:Male; D020714:Maximum Tolerated Dose; D008875:Middle Aged; D011467:Prostate / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D047368:Tumor Burden; D014463:Ultrasonography; D014521:Urethra / Q000033:anatomy & histology / Q000000981:diagnostic imaging* / Q000528:radiation effects; D014546:Urinary Catheterization / Q000295:instrumentation*