title: A comprehensive review of MR imaging changes following radiosurgery to 500 brain metastases.
abstract: OBJECTIVE
  Stereotactic radiosurgery is known to control 85%-95% of intracranial metastatic lesions during a median survival of 6-8 months. However, with the advent of newer systemic cancer therapies, survival is improving; this change mandates a longitudinal quantitative analysis of the radiographic response of brain metastases to radiosurgery.
  
  
  METHODS
  MR imaging of 516 metastases in 120 patients treated with GK-SRS from June 2006 to December 2009 was retrospectively reviewed. Lesion volume at initial treatment and each follow-up was calculated by using the following formula: length × width × height / 2. Volume changes were correlated with patient demographics, histopathology, and radiation treatment variables.
  
  
  RESULTS
  Thirty-two percent of lesions increased in volume following radiosurgery. Clinically, this translated into 54% of patients having ≥1 of their lesions increase in size. This increase begins at 6 weeks and can last beyond 15 months' post-SRS. Male sex (P = .002), mean voxel dose <37 Gy (P = .009), and initial treatment volume >500 mm(3) (P < .001) are associated with posttreatment increases in tumor size. Median survival following radiosurgery was 9.5 months for patients with all lesions exhibiting stable/decreased volumes, >18.4 months for patients with all lesions exhibiting increased volumes, and 16.4 months for patients with mixed lesional responses.
  
  
  CONCLUSIONS
  Most metastatic lesions are stable or smaller in size during the first 36 months post-SRS. However, a transient increase in volume is seen in approximately one-third of lesions. Sex, treatment dose, initial lesion size, and histopathology all correlate with variations in lesion volume post-SRS. The longer the patient survives, the more likely an increase in lesion size will be seen on follow-up imaging.
authors.affiliation: Department of Neurosurgery, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
authors.forename: T R
authors.initials: TR
authors.lastname: Patel
authors.forename: B J
authors.initials: BJ
authors.lastname: McHugh
authors.forename: W L
authors.initials: WL
authors.lastname: Bi
authors.forename: F J
authors.initials: FJ
authors.lastname: Minja
authors.forename: J P S
authors.initials: JP
authors.lastname: Knisely
authors.forename: V L
authors.initials: VL
authors.lastname: Chiang
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001932:Brain Neoplasms / Q000473:pathology / Q000556:secondary / Q000601:surgery; D003237:Connecticut / Q000453:epidemiology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D016634:Radiosurgery / Q000706:statistics & numerical data*; D015203:Reproducibility of Results; D018570:Risk Assessment; D012307:Risk Factors; D012680:Sensitivity and Specificity; D016019:Survival Analysis; D015996:Survival Rate