title: Split dose carbon ion irradiation of the rat spinal cord: Dependence of the relative biological effectiveness on dose and linear energy transfer.
abstract: OBJECTIVE
  To measure the relative biological effectiveness (RBE) of carbon ions relative to 15 MeV photons in the rat spinal cord for different linear energy transfers (LET) to validate model calculations.
  
  
  METHODS
  The cervical spinal cord of rats was irradiated with 2 fractions of carbon ions at six positions of a 6 cm spread-out Bragg-peak (SOBP, 16-99 keV/μm). TD50-values (dose at 50% complication probability) were determined from dose-response curves for the endpoint radiation induced myelopathy (paresis grade II) within 300 days after irradiation. Using previously published TD50-values for photons (Karger et al., 2006; Debus et al., 2003), RBE-values were determined and compared with predictions of two versions of the local effect model (LEM I and IV).
  
  
  RESULTS
  TD50-values for paresis grade II were 26.7 ± 0.4 Gy (16 keV/μm), 24.0 ± 0.3 Gy (21 keV/μm), 22.5 ± 0.3 Gy (36 keV/μm), 20.1 ± 1.2 Gy (45 keV/μm), 17.7 ± 0.3 Gy (66 keV/μm), and 14.9 ± 0.3 Gy (99 keV/μm). RBE-values increased from 1.28 ± 0.03 (16 keV/μm) up to 2.30 ± 0.06 at 99 keV/μm. At the applied high fractional doses, LEM I fits best at 16 keV/μm and deviates progressively toward higher LETs while LEM IV agrees best at 99 keV/μm and shows increasing deviations, especially below 66 keV/μm.
  
  
  CONCLUSIONS
  The measured data improve the knowledge on the accuracy of RBE-calculations for carbon ions.
authors.affiliation: Dept. of Radiation Oncology, University Hospital of Heidelberg, Germany; Dept. of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany. Electronic address: m.saager@dkfz.de.
authors.forename: Maria
authors.initials: M
authors.lastname: Saager
authors.affiliation: Dept. of Radiation Oncology, University Hospital of Heidelberg, Germany; Dept. of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
authors.forename: Christin
authors.initials: C
authors.lastname: Glowa
authors.affiliation: Clinical Cooperation Unit Molecular Radiooncology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Peschke
authors.affiliation: Heidelberg Ion Beam Therapy Center (HIT), Heidelberg, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Brons
authors.affiliation: Dept. of Biophysics, Helmholtz Center for Heavy Ion Research (GSI), Darmstadt, Germany.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Grün
authors.affiliation: Dept. of Biophysics, Helmholtz Center for Heavy Ion Research (GSI), Darmstadt, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Scholz
authors.affiliation: Dept. of Radiation Oncology, University Hospital of Heidelberg, Germany; Clinical Cooperation Unit Molecular Radiooncology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
authors.forename: Peter E
authors.initials: PE
authors.lastname: Huber
authors.affiliation: Dept. of Radiation Oncology, University Hospital of Heidelberg, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Debus
authors.affiliation: Dept. of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
authors.forename: Christian P
authors.initials: CP
authors.lastname: Karger
mesh_terms: D000818:Animals; D004307:Dose-Response Relationship, Radiation; D005260:Female; D063193:Heavy Ion Radiotherapy / Q000379:methods*; D018499:Linear Energy Transfer; D011879:Radiotherapy Dosage; D051381:Rats; D017207:Rats, Sprague-Dawley; D012062:Relative Biological Effectiveness; D013116:Spinal Cord / Q000528:radiation effects*
keywords: Carbon ion radiotherapy; Dose response; Linear energy transfer (LET); Relative biological effectiveness (RBE)