title: MR and CT image fusion for postimplant analysis in permanent prostate seed implants.
abstract: OBJECTIVE
  To compare the outcome of two different image-based postimplant dosimetry methods in permanent seed implantation.
  
  
  METHODS
  Between October 1999 and October 2002, 150 patients with low-risk prostate carcinoma were treated with (125)I and (103)Pd in our institution. A CT-MRI image fusion protocol was used in 21 consecutive patients treated with exclusive brachytherapy. The accuracy and reproducibility of the method was calculated, and then the CT-based dosimetry was compared with the CT-MRI-based dosimetry using the dose-volume histogram (DVH) related parameters recommended by the American Brachytherapy Society and the American Association of Physicists in Medicine.
  
  
  RESULTS
  Our method for CT-MRI image fusion was accurate and reproducible (median shift <1 mm). Differences in prostate volume were found, depending on the image modality used. Quality assurance DVH-related parameters strongly depended on the image modality (CT vs. CT-MRI): V(100) = 82% vs. 88%, p < 0.05. D(90) = 96% vs. 115%, p < 0.05. Those results depend on the institutional implant technique and reflect the importance of lowering inter- and intraobserver discrepancies when outlining prostate and organs at risk for postimplant dosimetry.
  
  
  CONCLUSIONS
  Computed tomography-MRI fused images allow accurate determination of prostate size, significantly improving the dosimetric evaluation based on DVH analysis. This provides a consistent method to judge a prostate seed implant's quality.
authors.affiliation: Division of Radiation Oncology, European Institute of Oncology, Milan, Italy. apolo@csub.scs.es
authors.forename: Alfredo
authors.initials: A
authors.lastname: Polo
authors.forename: Federica
authors.initials: F
authors.lastname: Cattani
authors.forename: Andrea
authors.initials: A
authors.lastname: Vavassori
authors.forename: Daniela
authors.initials: D
authors.lastname: Origgi
authors.forename: Gaetano
authors.initials: G
authors.lastname: Villa
authors.forename: Hugo
authors.initials: H
authors.lastname: Marsiglia
authors.forename: Massimo
authors.initials: M
authors.lastname: Bellomi
authors.forename: Giampiero
authors.initials: G
authors.lastname: Tosi
authors.forename: Ottavio
authors.initials: O
authors.lastname: De Cobelli
authors.forename: Roberto
authors.initials: R
authors.lastname: Orecchia
mesh_terms: D000368:Aged; D000465:Algorithms; D001918:Brachytherapy / Q000379:methods*; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010165:Palladium / Q000627:therapeutic use; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D011868:Radioisotopes / Q000627:therapeutic use; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D007457:Iodine Radioisotopes; D011868:Radioisotopes; D010165:Palladium