Comparison of urethral diameters for calculating the urethral dose after permanent prostate brachytherapy.
OBJECTIVE
No studies have yet evaluated the effects of a dosimetric analysis for different urethral volumes. We therefore evaluated the effects of a dosimetric analysis to determine the different urethral volumes.


METHODS
This study was based on computed tomography/magnetic resonance imaging (CT/MRI) combined findings in 30 patients who had undergone prostate brachytherapy. Postimplant CT/MRI scans were performed 30 days after the implant. The urethra was contoured based on its diameter (8, 6, 4, 2, and 0 mm). The total urethral volume-in cubic centimeters [UrV150/200(cc)] and percent (UrV150%/200%), of the urethra receiving 150% or 200% of the prescribed dose-and the doses (UrD90/30/5) in Grays to 90%, 30%, and 5% of the urethral volume were measured based on the urethral diameters.


RESULTS
The UrV150(cc) and UrD30 were statistically different between the of 8-, 6-, 4-, 2-, and 0-mm diameters, whereas the UrD5 was statistically different only between the 8-, 6-, and 4-mm diameters. Especially for UrD5, there was an approximately 40-Gy difference between the mean values for the 8- and 0-mm diameters.


CONCLUSIONS
We recommend that the urethra should be contoured as a 4- to 6-mm diameter circle or one side of a triangle of 5-7 mm. By standardizing the urethral diameter, the urethral dose will be less affected by the total urethral volume.
Tanaka
Osamu
O
Department of Radiology, Gifu University School of Medicine, 1-1 Yanagido, Gifu, 501-1194, Japan. osa-mu@umin.ac.jp
Hayashi
Shinya
S
Matsuo
Masayuki
M
Nakano
Masahiro
M
Kubota
Yasuaki
Y
Maeda
Sunaho
S
Ohtakara
Kazuhiro
K
Deguchi
Takashi
T
Hoshi
Hiroaki
H
D001918:Brachytherapy; D003287:Contrast Media; D019786:Gadolinium DTPA; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D011446:Prospective Studies; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D014057:Tomography, X-Ray Computed; D018084:Ultrasonography, Interventional; D014521:Urethra / Q000033:anatomy & histology* / Q000528:radiation effects*
D003287:Contrast Media; D019786:Gadolinium DTPA
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