title: DCEMRI monitoring of canine tumors during fractionated radiotherapy.
abstract: OBJECTIVE
  To monitor the contrast enhancement in spontaneous canine tumors during fractionated radiotherapy by Dynamic Contrast Enhanced Magnetic Resonance Imaging (DCEMRI).
  
  
  METHODS
  Six dogs with tumors in the oral or nasal cavity received fractionated conformal radiotherapy with 54 Gy given in 18 fractions. T1 weighted DCE imaging was performed prior to each treatment fraction. The tumor was manually delineated in the MR images following every imaging session, and the time dependence of the Relative Signal Intensity (RSI) in the tumor was extracted voxel by voxel. RSI images at the time of maximum enhancement were generated, in addition to images of the initial slope of the RSI curves. The dependence of the median RSI and median slope in the tumor on the accumulated radiation dose was investigated, and images obtained at different treatment fraction were compared by correlation analysis.
  
  
  RESULTS
  Five of the six tumors regressed during treatment. The dose dependence of the RSI varied between the tumors, with some showing an increase and others a decrease in RSI with dose. This was also the case for the initial slope of the RSI curves. The correlation between images acquired before the first treatment fraction and subsequent fractions was in general low, and decreased significantly with accumulated radiation dose for five of six tumors.
  
  
  CONCLUSIONS
  Large individual variations in the dose response of tumor contrast enhancement were found. Decreasing image correlation resulted both from tumor regression and intratumoral changes in the RSI distribution during treatment. These findings may have consequences for treatment design in biological image-guided radiotherapy.
authors.affiliation: Department of Radiation Biology, Institute for Cancer Research, Rikshospitalet University Hospital, Oslo, Norway. aste.sovik@fys.uio.no
authors.forename: Aste
authors.initials: A
authors.lastname: Søvik
authors.forename: Hege
authors.initials: H
authors.lastname: Kippenes Skogmo
authors.forename: Øyvind S
authors.initials: ØS
authors.lastname: Bruland
authors.forename: Dag
authors.initials: D
authors.lastname: Rune Olsen
authors.forename: Eirik
authors.initials: E
authors.lastname: Malinen
mesh_terms: D000818:Animals; D003287:Contrast Media; D004285:Dogs; D005260:Female; D006258:Head and Neck Neoplasms / Q000175:diagnosis / Q000532:radiotherapy; D007089:Image Enhancement; D007206:Individuality; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009369:Neoplasms / Q000175:diagnosis* / Q000532:radiotherapy*; D020266:Radiotherapy, Conformal
chemical_list: D003287:Contrast Media