Comparison of real-time intraoperative ultrasound-based dosimetry with postoperative computed tomography-based dosimetry for prostate brachytherapy.
OBJECTIVE
To evaluate whether real-time intraoperative ultrasound (US)-based dosimetry can replace conventional postoperative computed tomography (CT)-based dosimetry in prostate brachytherapy.


METHODS
Between December 2001 and November 2002, 82 patients underwent (103)Pd prostate brachytherapy. An interplant treatment planning system was used for real-time intraoperative transrectal US-guided treatment planning. The dose distribution was updated according to the estimated seed position to obtain the dose-volume histograms. Postoperative CT-based dosimetry was performed a few hours later using the Theraplan-Plus treatment planning system. The dosimetric parameters obtained from the two imaging modalities were compared.


RESULTS
The results of this study revealed correlations between the US- and CT-based dosimetry. However, large variations were found in the implant-quality parameters of the two modalities, including the doses covering 100%, 90%, and 80% of the prostate volume and prostate volumes covered by 100%, 150%, and 200% of the prescription dose. The mean relative difference was 38% and 16% for doses covering 100% and 90% of the prostate volume and 10% and 21% for prostate volumes covered by 100% and 150% of the prescription dose, respectively. The CT-based volume covered by 200% of the prescription dose was about 30% greater than the US-based one. Compared with CT-based dosimetry, US-based dosimetry significantly underestimated the dose to normal organs, especially for the rectum. The average US-based maximal dose and volume covered by 100% of the prescription dose for the rectum was 72 Gy and 0.01 cm(3), respectively, much lower than the 159 Gy and 0.65 cm(3) obtained using CT-based dosimetry.


CONCLUSIONS
Although dosimetry using intraoperative US-based planning provides preliminary real-time information, it does not accurately reflect the postoperative CT-based dosimetry. Until studies have determined whether US-based dosimetry or postoperative CT-based dosimetry can better predict patient outcomes, the American Brachytherapy Society recommendation of CT-based postimplant dosimetry should remain the standard of care.
Nag
Subir
S
Department of Radiation Medicine, The Ohio State University, Columbus, OH 43210, USA.
Shi
Peipei
P
Liu
Bingren
B
Gupta
Nilendu
N
Bahnson
Robert R
RR
Wang
Jian Z
JZ
D001918:Brachytherapy / Q000379:methods* / Q000592:standards; D006801:Humans; D007432:Intraoperative Period; D008297:Male; D010165:Palladium / Q000627:therapeutic use; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D011868:Radioisotopes / Q000627:therapeutic use; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D012007:Rectum; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography; D014521:Urethra
D011868:Radioisotopes; D010165:Palladium