Differences between intraoperative ultrasound-based dosimetry and postoperative computed tomography-based dosimetry for permanent interstitial prostate brachytherapy
Received 18 June 2009; received in revised form 31 August 2009; accepted 11 September 2009. published online 01 February 2010.
Abstract
Purpose
To compare the results of intraoperative ultrasound (US)-based dosimetry with those of postimplant computed tomography (CT)-based dosimetry after 125I prostate brachytherapy.
Methods and Materials
Subjects comprised 160 patients who underwent prostate brachytherapy using 125I seed implants. Prescribed dose was set as 145Gy 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 (CT1) and Day 30 (CT30).
Results
Mean minimal dose received by 90% of prostate volume was 133.7%, 115.6%, and 125.8% of the prescribed dose on US, CT1, and CT30, 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 1.02mL on US, CT1, and CT30, respectively. Rectal parameters tended to be underestimated on US relative to CT30-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, CT1, and CT30. 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.
1Department of Radiology, Kitasato University School of Medicine, Kitasato, Sagamihara, Japan
2Department of Radiology, Iwate Medical University, Morioka, Iwate, Japan
3Department of Urology, Kitasato University School of Medicine, Kitasato, Sagamihara, Japan
4Department of Urology, Iwate Medical University, Morioka, Iwate, Japan
5Division of Radiation Oncology, Kitasato University Hospital, Kitasato, Sagamihara, Japan
Corresponding author. Department of Radiology, Kitasato University School of Medicine, 1-15-1 Kitasato, Sagamihara, Japan. Tel.: +81-778-8453; fax: +81-778-9436.
Conflicts of interest: Any actual or potential conflicts of interest do not exist in this report.
ABSTRACT