title: Water Exchange Rate Constant as a Biomarker of Treatment Efficacy in Patients With Brain Metastases Undergoing Stereotactic Radiosurgery.
abstract: This study was designed to evaluate whether changes in metastatic brain tumors after stereotactic radiosurgery (SRS) can be seen with quantitative MRI early after treatment.
  
  
  
  Using contrast-enhanced MRI, a 3-water-compartment tissue model consisting of intracellular (I), extracellular-extravascular (E), and vascular (V) compartments was used to assess the intra-extracellular water exchange rate constant (kIE), efflux rate constant (kep), and water compartment volume fractions (M0,I, M0,E, M0,V). In this prospective study, 19 patients were MRI-scanned before treatment and 1 week and 1 month after SRS. The change in model parameters between the pretreatment and 1-week posttreatment scans was correlated to the change in tumor volume between pretreatment and 1-month posttreatment scans.
  
  
  
  At 1 week kIEdifferentiated (P<.001) tumors that had partial response from tumors with stable and progressive disease, and a high correlation (R=-0.76, P<.001) was observed between early changes in the kIEand tumor volume change 1 month after treatment. Other model parameters had lower correlation (M0,E) or no correlation (kep, M0,V).
  
  
  
  This is the first study that measured kIEearly after SRS, and it found that early changes in kIE(1 week after treatment) highly correlated with long-term tumor response and could predict the extent of tumor shrinkage at 1 month after SRS.
authors.affiliation: Medical Biophysics, University of Toronto, Toronto, Ontario, Canada; Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada. Electronic address: hatef.mehrabian@sri.utoronto.ca.
authors.forename: Hatef
authors.initials: H
authors.lastname: Mehrabian
authors.affiliation: Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada.
authors.forename: Kimberly L
authors.initials: KL
authors.lastname: Desmond
authors.affiliation: Research Imaging Centre, Centre for Addiction and Mental Health, Toronto, Ontario, Canada.
authors.forename: Sofia
authors.initials: S
authors.lastname: Chavez
authors.affiliation: Computer Science Department, University College London, London, United Kingdom.
authors.forename: Colleen
authors.initials: C
authors.lastname: Bailey
authors.affiliation: Neurosurgery and Pediatric Neurosurgery, Medical University, Lublin, Poland.
authors.forename: Radoslaw
authors.initials: R
authors.lastname: Rola
authors.affiliation: Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada; Radiation Oncology, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada.
authors.forename: Arjun
authors.initials: A
authors.lastname: Sahgal
authors.affiliation: Medical Biophysics, University of Toronto, Toronto, Ontario, Canada; Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada; Radiation Oncology, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Czarnota
authors.affiliation: Radiation Oncology, Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada.
authors.forename: Hany
authors.initials: H
authors.lastname: Soliman
authors.affiliation: Medical Biophysics, University of Toronto, Toronto, Ontario, Canada; Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada.
authors.forename: Anne L
authors.initials: AL
authors.lastname: Martel
authors.affiliation: Medical Biophysics, University of Toronto, Toronto, Ontario, Canada; Physical Sciences, Sunnybrook Research Institute, Toronto, Ontario, Canada; Neurosurgery and Pediatric Neurosurgery, Medical University, Lublin, Poland.
authors.forename: Greg J
authors.initials: GJ
authors.lastname: Stanisz
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017209:Apoptosis; D014408:Biomarkers, Tumor / Q000378:metabolism*; D001834:Body Water / Q000000981:diagnostic imaging / Q000378:metabolism; D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism / Q000532:radiotherapy* / Q000556:secondary*; D003287:Contrast Media; D018450:Disease Progression; D045604:Extracellular Fluid / Q000000981:diagnostic imaging / Q000378:metabolism*; D005260:Female; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D011446:Prospective Studies; D016634:Radiosurgery / Q000379:methods*; D013997:Time Factors; D016896:Treatment Outcome; D047368:Tumor Burden / Q000502:physiology / Q000528:radiation effects
chemical_list: D014408:Biomarkers, Tumor; D003287:Contrast Media