Real-time Intraoperative Computed Tomography Assessment of Quality of Permanent Interstitial Seed Implantation for Prostate Cancer

Abstract

To evaluate the use of real-time kilovoltage cone-beam computed tomography (CBCT) during prostate brachytherapy for intraoperative dosimetric assessment and correcting deficient dose regions. A total of 20 patients were evaluated intraoperatively with a mobile CBCT unit immediately after implantation while still anesthetized. The source detector system was enclosed in a circular CT-like geometry with a bore that accommodates patients in the lithotomy position. After seed deposition, the CBCT scans were obtained. The dosimetry was evaluated and compared with the standard postimplantation CT-based assessment. In 8 patients, the deposited seeds were localized in the intraoperative CBCT frame of reference and registered to the intraoperative transrectal ultrasound images. With this information, a second intraoperative plan was generated to ascertain whether additional seeds were needed to achieve the planned prescription dose. The final dosimetry was compared with the postimplantation scan assessment. The mean differences between the dosimetric parameters from the intraoperative CBCT and postimplant CT scans were < .5% for percentage of volume receiving 100% of the prescription dose, minimal dose received by 90% of the prostate, and percentage of volume receiving 150% of the prescription dose. The minimal dose received by 5% (maximal dose) of the urethra differed by 8% on average and for the rectum an average difference of approximately 18% was observed. After fusion of the implanted seed coordinates from the intraoperative CBCT scans to the intraoperative transrectal ultrasound images, the dosimetric outcomes were not significantly different from the postimplantation CT dosimetric results. Intraoperative CT-based dosimetric evaluation of prostate permanent seed implantation before anesthesia reversal is feasible and might avert misadministration of dose delivery. The dosimetric measurements using the intraoperative CBCT scans were dependable and correlated well with the postimplant diagnostic CT findings.