title: Temporal lobe reactions after carbon ion radiation therapy: comparison of relative biological effectiveness-weighted tolerance doses predicted by local effect models I and IV.
abstract: OBJECTIVE
  To compare the relative biological effectiveness (RBE)-weighted tolerance doses for temporal lobe reactions after carbon ion radiation therapy using 2 different versions of the local effect model (LEM I vs LEM IV) for the same patient collective under identical conditions.
  
  
  METHODS
  In a previous study, 59 patients were investigated, of whom 10 experienced temporal lobe reactions (TLR) after carbon ion radiation therapy for low-grade skull-base chordoma and chondrosarcoma at Helmholtzzentrum für Schwerionenforschung (GSI) in Darmstadt, Germany in 2002 and 2003. TLR were detected as visible contrast enhancements on T1-weighted MRI images within a median follow-up time of 2.5 years. Although the derived RBE-weighted temporal lobe doses were based on the clinically applied LEM I, we have now recalculated the RBE-weighted dose distributions using LEM IV and derived dose-response curves with Dmax,V-1 cm³ (the RBE-weighted maximum dose in the remaining temporal lobe volume, excluding the volume of 1 cm³ with the highest dose) as an independent dosimetric variable. The resulting RBE-weighted tolerance doses were compared with those of the previous study to assess the clinical impact of LEM IV relative to LEM I.
  
  
  RESULTS
  The dose-response curve of LEM IV is shifted toward higher values compared to that of LEM I. The RBE-weighted tolerance dose for a 5% complication probability (TD5) increases from 68.8 ± 3.3 to 78.3 ± 4.3 Gy (RBE) for LEM IV as compared to LEM I.
  
  
  CONCLUSIONS
  LEM IV predicts a clinically significant increase of the RBE-weighted tolerance doses for the temporal lobe as compared to the currently applied LEM I. The limited available photon data do not allow a final conclusion as to whether RBE predictions of LEM I or LEM IV better fit better clinical experience in photon therapy. The decision about a future clinical application of LEM IV therefore requires additional analysis of temporal lobe reactions in a comparable photon-treated collective using the same dosimetric variable as in the present study.
authors.affiliation: Department of Radiation Oncology and Radiation Therapy, Heidelberg University Hospital, Heidelberg, Germany. Electronic address: clarissa.gillmann@med.uni-heidelberg.de.
authors.forename: Clarissa
authors.initials: C
authors.lastname: Gillmann
authors.affiliation: Department of Radiation Oncology and Radiation Therapy, Heidelberg University Hospital, Heidelberg, Germany; Heidelberg Ion Beam Therapy Center (HIT), Heidelberg, Germany; Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Jäkel
authors.affiliation: Department of Radiation Oncology and Radiation Therapy, Heidelberg University Hospital, Heidelberg, Germany.
authors.forename: Ingmar
authors.initials: I
authors.lastname: Schlampp
authors.affiliation: Department 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: D000293:Adolescent; D000328:Adult; D000368:Aged; D002244:Carbon / Q000737:chemistry; D002813:Chondrosarcoma / Q000532:radiotherapy*; D002817:Chordoma / Q000532:radiotherapy*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D063193:Heavy Ion Radiotherapy / Q000379:methods*; D006801:Humans; D007477:Ions; D008297:Male; D008875:Middle Aged; D017785:Photons; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012062:Relative Biological Effectiveness; D012189:Retrospective Studies; D019292:Skull Base Neoplasms / Q000532:radiotherapy*; D013702:Temporal Lobe / Q000528:radiation effects*; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D007477:Ions; D002244:Carbon