Differences between intraoperative ultrasound-based dosimetry and postoperative computed tomography-based dosimetry for permanent interstitial prostate brachytherapy.
OBJECTIVE
To compare the results of intraoperative ultrasound (US)-based dosimetry with those of postimplant computed tomography (CT)-based dosimetry after (125)I prostate brachytherapy.


METHODS
Subjects comprised 160 patients who underwent prostate brachytherapy using (125)I seed implants. Prescribed dose was set as 145 Gy to the periphery of the prostate. Implantation was performed using an intraoperative interactive technique. Postimplant dosimetry was performed on Days 1 and 30 after implantation using CT. Dosimetric results for the prostate, urethra, and rectum were compared among intraoperative US and CT on Day 1 (CT(1)) and Day 30 (CT(30)).


RESULTS
Mean minimal dose received by 90% of prostate volume was 133.7%, 115.6%, and 125.8% of the prescribed dose on US, CT(1), and CT(30), respectively: This value temporarily decreased on Day 1 and increased on Day 30. Other parameters for the prostate and urethra showed similar trends. Conversely, mean rectal volume receiving 100% of the prescribed dose was 0.69, 0.46, and 1.02 mL on US, CT(1), and CT(30), respectively. Rectal parameters tended to be underestimated on US relative to CT(30)-based dosimetry. A positive linear relationship was identified between US and CT observations for every prostate parameter and the dose covering 30% of the urethra.


CONCLUSIONS
Our results demonstrate significant differences between dosimetric parameters obtained by US, CT(1), and CT(30). However, significant correlations also exist between US and CT, at least in prostate and urethral parameters. Clarification of the degrees of difference might make US planning more feasible.
Ishiyama
Hiromichi
H
Department of Radiology, Kitasato University School of Medicine, Kitasato, Sagamihara, Japan. hishiyam@kitasato-u.ac.jp
Nakamura
Ryuji
R
Satoh
Takefumi
T
Tanji
Susumu
S
Uemae
Mineko
M
Baba
Shiro
S
Hayakawa
Kazushige
K
D000368:Aged; D000369:Aged, 80 and over; D006801:Humans; D007430:Intraoperative Care / Q000379:methods; D008297:Male; D008875:Middle Aged; D011182:Postoperative Care / Q000379:methods; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000532:radiotherapy*; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014463:Ultrasonography / Q000379:methods*