title: Impact of MRI-based postimplant dosimetric assessment in prostate brachytherapy using contrast-enhanced T1-weighted images.
abstract: OBJECTIVE
  To compare contrast-enhanced T1-weighted (CE-T1WI) magnetic resonance imaging (MRI) with computed tomography (CT) for postimplant dosimetry and seed recognition in prostate brachytherapy.
  
  
  METHODS
  A total of 245 patients who received (125)I prostate brachytherapy with or without external beam radiotherapy were enrolled. For postimplant analysis, CT and MRI scans were obtained at 1 month after seed implantation. For MRI-based dosimetry, T2-weighted images were fused with the CE-T1WI; the prostate was delineated on the T2-weighted images, and the seed detection was performed manually on the CE-T1WI. In CT-based dosimetry, the seed detection was essentially performed automatically. The dosimetric results obtained by MRI-based and CT-based dosimetry were compared.
  
  
  RESULTS
  The mean prostate D(90) (the minimum dose received by 90% of the prostate volume) estimated by MRI-based and CT-based dosimetry were 113% and 115%, respectively, with no significant difference. The mean prostate V(100) (the percent volume of the postimplant prostate receiving 100% of the prescribed dose) estimated by MRI-based and CT-based dosimetry were 95.2% and 95.8%, respectively, again with no significant difference. The mean prostate V(150) (the percent volume of the postimplant prostate receiving 150% of the prescribed dose) estimated by MRI-based and CT-based dosimetry were 52.8% and 57.0%, respectively (p<0.01). In all of the 35 patients (14%) in whom the MRI-based V(150) were at least 10% lower than the CT-based results, the seed detection by CT-based dosimetry was overestimated in highly seed-clustered areas or in the areas close to calcifications because of reconstruction artifacts in CT images.
  
  
  CONCLUSIONS
  MRI-based dosimetry using CE-T1WI appears to be acceptable. Our results suggest that MRI-based dosimetry is a practical method for estimation of the higher dose distribution, especially if seeds are clustered together or when they are close to calcifications.
authors.affiliation: Department of Radiology, Keio University School of Medicine, Tokyo, Japan. ohashi@rad.med.keio.ac.jp
authors.forename: Toshio
authors.initials: T
authors.lastname: Ohashi
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Momma
authors.forename: Shoji
authors.initials: S
authors.lastname: Yamashita
authors.forename: Katsumi
authors.initials: K
authors.lastname: Nagatsuma
authors.forename: Kunimitsu
authors.initials: K
authors.lastname: Kanai
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Kitagawa
authors.forename: Shinichi
authors.initials: S
authors.lastname: Takahashi
authors.forename: Takashi
authors.initials: T
authors.lastname: Hanada
authors.forename: Atsunori
authors.initials: A
authors.lastname: Yorozu
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Shigematsu
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001918:Brachytherapy / Q000379:methods / Q000706:statistics & numerical data*; D003287:Contrast Media; D019786:Gadolinium DTPA; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007564:Japan / Q000453:epidemiology; D008279:Magnetic Resonance Imaging / Q000379:methods / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011471:Prostatic Neoplasms / Q000453:epidemiology / Q000473:pathology* / Q000532:radiotherapy*; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D061089:Radiotherapy, Image-Guided / Q000379:methods / Q000706:statistics & numerical data*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016896:Treatment Outcome
chemical_list: D003287:Contrast Media; D019786:Gadolinium DTPA