title: Limitations of dynamic contrast-enhanced MRI in monitoring radiation-induced changes in the fraction of radiobiologically hypoxic cells in human melanoma xenografts.
abstract: OBJECTIVE
  To investigate the potential of gadopentetate dimeglumine (Gd-DTPA)-based dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in detecting radiation-induced changes in the fraction of radiobiologically hypoxic cells in A-07 human melanoma xenografts.
  
  
  METHODS
  A-07 tumors were randomly assigned to an unirradiated control group or a group given a single radiation dose of 20 Gy. DCE-MRI and measurement of fraction of hypoxic cells were performed immediately before and 24 h after the radiation exposure. Tumor images of E . F (E is the initial extraction fraction of Gd-DTPA and F is blood perfusion) and lambda (lambda is proportional to extracellular volume fraction) were produced by subjecting DCE-MRI series to Kety analysis. Fraction of hypoxic cells was measured by using a radiobiological assay based on the paired survival curve method.
  
  
  RESULTS
  Fraction of radiobiologically hypoxic cells was higher in irradiated tumors (26.2+/-5.8%) than in unirradiated tumors (7.5+/-2.7%) by a factor of 3.5+/-1.5 (P=0.0093), whereas only minor radiation-induced changes in E . F and lambda could be detected.
  
  
  CONCLUSIONS
  DCE-MRI does not seem to offer insight into the changes in fraction of radiobiologically hypoxic cells occurring in A-07 tumors within 24 h after irradiation with 20 Gy.
authors.affiliation: Group of Radiation Biology and Tumor Physiology, Department of Radiation Biology, Institute for Cancer Research, Norwegian Radium Hospital, Montebello, Oslo, Norway.
authors.forename: Ilana C
authors.initials: IC
authors.lastname: Benjaminsen
authors.forename: Elin A
authors.initials: EA
authors.lastname: Melås
authors.forename: Berit S
authors.initials: BS
authors.lastname: Mathiesen
authors.forename: Einar K
authors.initials: EK
authors.lastname: Rofstad
mesh_terms: D000818:Animals; D015687:Cell Hypoxia / Q000528:radiation effects*; D045744:Cell Line, Tumor; D003287:Contrast Media; D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D005260:Female; D019786:Gadolinium DTPA; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008545:Melanoma / Q000473:pathology* / Q000503:physiopathology* / Q000532:radiotherapy; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D011829:Radiation Dosage
chemical_list: D003287:Contrast Media; D019786:Gadolinium DTPA