title: DCEMRI of spontaneous canine tumors during fractionated radiotherapy: a pharmacokinetic analysis.
abstract: OBJECTIVE
  To estimate pharmacokinetic parameters from dynamic contrast-enhanced magnetic resonance (DCEMR) images of spontaneous canine tumors taken during the course of fractionated radiotherapy, and to quantify treatment-induced changes in these parameters.
  
  
  METHODS
  Six dogs with tumors in the oral or nasal cavity received fractionated conformal radiotherapy with 54 Gy given in 18 fractions. T(1)-weighted DCEMR imaging was performed prior to each treatment fraction. Time-intensity curves in the tumor were extracted voxel-by-voxel, and were fitted to the Brix pharmacokinetic model. The dependence of the pharmacokinetic parameters on the accumulated radiation dose was calculated.
  
  
  RESULTS
  The Brix model reproduced the time-intensity curves well. A reduction in the k(ep) parameter with accumulated radiation dose was found for five (three significant) out of six cases, while the results for the A parameter were less consistent. Both pre-treatment k(ep) and the change in k(ep) with accumulated dose correlated significantly with tumor regression.
  
  
  CONCLUSIONS
  Pharmacokinetic parameters derived from DCEMR images taken during fractionated radiotherapy may predict response to radiotherapy. This may potentially impact on patient stratification and monitoring of treatment response for image-guided treatment strategies.
authors.affiliation: Department of Radiation Biology, Oslo University Hospital, Oslo, Norway. aste.sovik@fys.uio.no
authors.forename: Ste
authors.initials: S
authors.lastname: Søvik
authors.forename: Hege Kippenes
authors.initials: HK
authors.lastname: Skogmo
authors.forename: Erlend K F
authors.initials: EK
authors.lastname: Andersen
authors.forename: Øyvind S
authors.initials: ØS
authors.lastname: Bruland
authors.forename: Dag Rune
authors.initials: DR
authors.lastname: Olsen
authors.forename: Eirik
authors.initials: E
authors.lastname: Malinen
mesh_terms: D000818:Animals; D003287:Contrast Media / Q000493:pharmacokinetics; D004283:Dog Diseases / Q000175:diagnosis / Q000532:radiotherapy*; D004285:Dogs; D019583:Dose Fractionation, Radiation; D019786:Gadolinium DTPA / Q000493:pharmacokinetics; D008279:Magnetic Resonance Imaging / Q000662:veterinary*; D009062:Mouth Neoplasms / Q000175:diagnosis / Q000532:radiotherapy / Q000662:veterinary*; D009669:Nose Neoplasms / Q000175:diagnosis / Q000532:radiotherapy / Q000662:veterinary*; D011879:Radiotherapy Dosage / Q000662:veterinary; D020266:Radiotherapy, Conformal / Q000662:veterinary*
chemical_list: D003287:Contrast Media; D019786:Gadolinium DTPA