AbstractID: 6954 Title: Comparison of 2-D and 3-D Intra-Operative Dosimetry of Prostate Seed Implants
A currently popular technique for prostate seed implants, 2-D Intra-Operative Dosimetry (2DIOD), relies
on needle placement data acquired from ultrasound during the procedure. The 2DIOD method assumes
that seeds are correctly deposited along the length of the needle. Observations suggest otherwise. We
have developed a 3-D Intra-Operative Dosimetry method (3DIOD), which fuses ultrasound and
fluoroscopy images by means of registration seeds and a cystoscopic verification of the prostate location.
As needles are inserted, the ultrasound provides the x-y location. As each seed is deposited, the x-z
position is obtained from the x-ray image relative to the registrations seeds. After correction for
registration, divergence, and magnification, each seed is uniquely identified in 3-dimensions relative to the
marker seeds, which are in turn fused to the prostate geometry. Seed, needle and contour corrections may
be made as the case proceeds. For 3DIOD, the mean and standard deviation of the error of the seed
identification in phantom studies was 1.4 +/- 0.7 mm, and is dependent on fluoroscopy image resolution.
Comparison of 2DIOD and 3DIOD techniques to CT based post plans was retrospectively performed
eleven patients. 3DIOD predicted the CT post-plan total gland coverage (V100) with an r-squared value
of 0.95, while 2DIOD had an r-squared value of 0.65. Excellent correlation between the 3DIOD method
and CT post-plans was observed. 3DIOD is significantly better than 2DIOD in predicting V100 (p<0.01).
The 3DIOD method uses already existing Ultrasound and Fluoroscopy equipment, and is cost effective at
providing real-time intraoperative implant dosimetry.