title: Assessment of irradiated brain metastases using dynamic contrast-enhanced magnetic resonance imaging.
abstract: BACKGROUND
  The purpose of this study was to evaluate the effect of stereotactic radiosurgery (SRS) on cerebral metastases using the transfer constant (K trans) assessed by dynamic contrast-enhanced (DCE) MRI. Furthermore, we aimed to evaluate the ability of K trans measurements to predict midterm tumor outcomes after SRS.
  
  
  METHODS
  The study received institutional review board approval, and informed consent was obtained from all subjects. Twenty-six adult patients with a total of 34 cerebral metastases underwent T1-weighted DCE MRI in a 1.5-T magnet at baseline (prior to SRS) and 4-8 weeks after treatment. Quantitative analysis of DCE MRI was performed by generating K trans parametric maps, and region-of-interest-based measurements were acquired for each metastasis. Conventional MRI was performed at least 16 weeks after SRS to assess midterm tumor outcome using volume variation.
  
  
  RESULTS
  The mean (±SD) K trans value was 0.13 ± 0.11 min(-1) at baseline and 0.08 ± 0.07 min(-1) after 4-8 weeks post-treatment (p < 0.001). The mean (±SD) total follow-up time was 7.9 ± 4.7 months. Seventeen patients (22 lesions) underwent midterm MRI. Of those, nine (41 %) lesions had progressed at the midterm follow-up. An increase in K trans after SRS was predictive of tumor progression (hazard ratio = 1.50; 95 % CI = 1.16-1.70, p < 0.001). An increase of 15 % in K trans showed a sensitivity of 78 % and a specificity of 85 % for the prediction of progression at midterm follow-up.
  
  
  CONCLUSIONS
  SRS was associated with a reduction of K trans values of the cerebral metastases in the early post-treatment period. Furthermore, K trans variation as assessed using DCE MRI may be helpful to predict midterm outcomes after SRS.
authors.affiliation: Department of Radiology, University of São Paulo, São Paulo, Brazil, daniela.ba@gmail.com.
authors.forename: Daniela B
authors.initials: DB
authors.lastname: Almeida-Freitas
authors.forename: Marco C
authors.initials: MC
authors.lastname: Pinho
authors.forename: Maria C G
authors.initials: MC
authors.lastname: Otaduy
authors.forename: Henrique F
authors.initials: HF
authors.lastname: Braga
authors.forename: Daniel
authors.initials: D
authors.lastname: Meira-Freitas
authors.forename: Claudia
authors.initials: C
authors.lastname: da Costa Leite
mesh_terms: D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000556:secondary* / Q000601:surgery*; D003287:Contrast Media; D018450:Disease Progression; D005260:Female; D019786:Gadolinium DTPA; D006801:Humans; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D016634:Radiosurgery; D012680:Sensitivity and Specificity
chemical_list: D003287:Contrast Media; D019786:Gadolinium DTPA