title: Carbon ion irradiation of the rat spinal cord: dependence of the relative biological effectiveness on linear energy transfer.
abstract: OBJECTIVE
  To measure the relative biological effectiveness (RBE) of carbon ions in the rat spinal cord as a function of linear energy transfer (LET).
  
  
  METHODS
  As an extension of a previous study, the cervical spinal cord of rats was irradiated with single doses of carbon ions at 6 positions of a 6-cm spread-out Bragg peak (16-99 keV/μm). The TD50 values (dose at 50% complication probability) were determined according to dose-response curves for the development of paresis grade 2 within an observation time of 300 days. The RBEs were calculated using TD50 for photons of our previous study.
  
  
  RESULTS
  Minimum latency time was found to be dose-dependent, but not significantly LET-dependent. The TD50 values for the onset of paresis grade 2 within 300 days were 19.5 ± 0.4 Gy (16 keV/μm), 18.4 ± 0.4 Gy (21 keV/μm), 17.7 ± 0.3 Gy (36 keV/μm), 16.1 ± 1.2 Gy (45 keV/μm), 14.6 ± 0.5 Gy (66 keV/μm), and 14.8 ± 0.5 Gy (99 keV/μm). The corresponding RBEs increased from 1.26 ± 0.05 (16 keV/μm) up to 1.68 ± 0.08 at 66 keV/μm. Unexpectedly, the RBE at 99 keV/μm was comparable to that at 66 keV/μm.
  
  
  CONCLUSIONS
  The data suggest a linear relation between RBE and LET at high doses for late effects in the spinal cord. Together with additional data from ongoing fractionated irradiation experiments, these data will provide an extended database to systematically benchmark RBE models for further improvements of carbon ion treatment planning.
authors.affiliation: Department of Radiation Oncology, University Hospital of Heidelberg, Heidelberg, Germany; Department of Medical Physics in Radiation Oncology, German Cancer Research Center, Heidelberg, Germany. Electronic address: m.saager@dkfz.de.
authors.forename: Maria
authors.initials: M
authors.lastname: Saager
authors.affiliation: Department of Radiation Oncology, University Hospital of Heidelberg, Heidelberg, Germany; Department of Medical Physics in Radiation Oncology, German Cancer Research Center, Heidelberg, Germany.
authors.forename: Christin
authors.initials: C
authors.lastname: Glowa
authors.affiliation: Clinical Cooperation Unit Molecular Radiooncology, German Cancer Research Center, 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: Department of Biophysics, Helmholtz Center for Heavy Ion Research (GSI), Darmstadt, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Scholz
authors.affiliation: Department of Radiation Oncology, University Hospital of Heidelberg, Heidelberg, Germany; Clinical Cooperation Unit Molecular Radiooncology, German Cancer Research Center, Heidelberg, Germany.
authors.forename: Peter E
authors.initials: PE
authors.lastname: Huber
authors.affiliation: Department of Radiation Oncology, University Hospital of Heidelberg, Heidelberg, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Debus
authors.affiliation: Department of Medical Physics in Radiation Oncology, German Cancer Research Center, Heidelberg, Germany.
authors.forename: Christian P
authors.initials: CP
authors.lastname: Karger
mesh_terms: D000818:Animals; D001835:Body Weight / Q000528:radiation effects; D002250:Carbon Radioisotopes; D002574:Cervical Vertebrae; D004307:Dose-Response Relationship, Radiation; D005260:Female; D018499:Linear Energy Transfer; D010291:Paresis / Q000209:etiology*; D017785:Photons; D051381:Rats; D017207:Rats, Sprague-Dawley; D012062:Relative Biological Effectiveness; D013116:Spinal Cord / Q000528:radiation effects*; D013997:Time Factors
chemical_list: D002250:Carbon Radioisotopes