title: Computing intraoperative dosimetry for prostate brachytherapy using TRUS and fluoroscopy.
abstract: OBJECTIVE
  There is a need to provide real-time dosimetric feedback during prostate brachytherapy based on the location of the implanted seeds. The objective of our approach is to develop a system to accurately locate seeds with minimal impact on the current protocol for prostate brachytherapy and without additional imaging equipment.
  
  
  METHODS
  A new approach for intraoperatively computing dosimetry for prostate brachytherapy is presented. The approach uses transrectal ultrasound (TRUS) and fluoroscopic images. A fluoroscopic image of the TRUS probe is required to register the fluoroscopic and ultrasound images. The C-arm is not moved during the procedure and all images are acquired from the same C-arm angles. A needle path is interpolated for each needle based on the location of the needle tip in TRUS images and the known entry point of the needle. Throughout the procedure, fluoroscopic images are acquired to determine the coronal plane coordinates of the seeds and the remaining coordinate of each seed is computed from the needle path. For accurate results, intraoperative seed motion tracking is advised and a method to achieve such tracking is also presented.
  
  
  RESULTS
  Experimentally, the TRUS and fluoroscopic images are registered with a mean and maximum error of 1.3 mm and 5.8 mm, respectively. In a phantom, 12 seeds are located using our approach and compared with the known locations, with a mean error in the x, y, and z direction of 0.96 mm, 0.33, and 0.68 mm, respectively, and a corresponding maximum error of 1.85 mm, 0.56 mm, and 1.63 mm. Experimental results show motion tracking in the y-direction with submillimeter accuracy. The feasibility of our approach is tested on five cases of clinical data using a semiautomated version of our system and the resulting dosimetry is compared with that found using postoperative computed tomography images. The D90 and V100 metrics computed using our approach and the computed tomography images differ by a maximum of 16.6% and 1.7%, respectively.
  
  
  CONCLUSIONS
  TRUS can be combined with single pose fluoroscopic images to compute delivered dose intraoperatively for prostate brachytherapy. Phantom results demonstrate the accuracy of the method and preliminary clinical results show its potential.
authors.affiliation: University of British Columbia, Electrical and Computer Engineering, 2356 Main Mall, Vancouver, Vancouver, BC V6T 1Z4, Canada.
authors.forename: Danny
authors.initials: D
authors.lastname: French
authors.forename: James
authors.initials: J
authors.lastname: Morris
authors.forename: Mira
authors.initials: M
authors.lastname: Keyes
authors.forename: Orcun
authors.initials: O
authors.lastname: Goksel
authors.forename: Septimiu
authors.initials: S
authors.lastname: Salcudean
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D007430:Intraoperative Care / Q000379:methods; D008297:Male; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011859:Radiography; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D014463:Ultrasonography / Q000379:methods*