title: Assessment of potential advantages of relevant ions for particle therapy: a model based study.
abstract: OBJECTIVE
  Different ion types offer different physical and biological advantages for therapeutic applications. The purpose of this work is to assess the advantages of the most commonly used ions in particle therapy, i.e., carbon ((12)C), helium ((4)He), and protons ((1)H) for different treatment scenarios.
  
  
  METHODS
  A treatment planning analysis based on idealized target geometries was performed using the treatment planning software TRiP98. For the prediction of the relative biological effectiveness (RBE) that is required for biological optimization in treatment planning the local effect model (LEM IV) was used. To compare the three ion types, the peak-to-entrance ratio (PER) was determined for the physical dose (PERPHY S), the RBE (PERRBE), and the RBE-weighted dose (PERBIO) resulting for different dose-levels, field configurations, and tissue types. Further, the dose contribution to artificial organs at risk (OAR) was assessed and a comparison of the dose distribution for the different ion types was performed for a patient with chordoma of the skull base.
  
  
  RESULTS
  The study showed that the advantages of the ions depend on the physical and biological properties and the interplay of both. In the case of protons, the consideration of a variable RBE instead of the clinically applied generic RBE of 1.1 indicates an advantage in terms of an increased PERRBE for the analyzed configurations. Due to the fact that protons show a somewhat better PERPHY S compared to helium and carbon ions whereas helium shows a higher PERRBE compared to protons, both protons and helium ions show a similar RBE-weighted dose distribution. Carbon ions show the largest variation of the PERRBE with tissue type and a benefit for radioresistant tumor types due to their higher LET. Furthermore, in the case of a two-field irradiation, an additional gain in terms of PERBIO is observed when using an orthogonal field configuration for carbon ions as compared to opposing fields. In contrast, for protons, the PERBIO is almost independent on the field configuration. Concerning the artificial lateral OAR, the volume receiving 20% of the prescribed RBE-weighted dose (V20) was reduced by over 35% using helium ions and by over 40% using carbon ions compared to protons. The analysis of the patient plan showed that protons, helium, and carbon ions are similar in terms of target coverage whereas the dose to the surrounding tissue is increasing from carbon ions toward protons. The mean dose to the brain stem can be reduced by more than 55% when using helium ions and by further 25% when using carbon ions instead of protons.
  
  
  CONCLUSIONS
  The comparison of the PERRBE and PERPHY S of the three ion types suggests a strong dependence of the advantages of the three ions on the dose-level, tissue type, and field configuration. In terms of conformity, i.e., dose to the normal tissue, a clear gain is expected using carbon or helium ions compared to protons.
authors: Department of Biophysics, GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt 64291, Germany; Institute of Medical Physics and Radiation Protection, University of Applied Sciences Gießen, Gießen 35390, Germany; and Medical Faculty of Philipps-University Marburg, Marburg 35032, Germany.
authors: Rebecca
authors: R
authors: Grün
authors: Department of Biophysics, GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt 64291, Germany.
authors: Thomas
authors: T
authors: Friedrich
authors: Department of Biophysics, GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt 64291, Germany.
authors: Michael
authors: M
authors: Krämer
authors: Institute of Medical Physics and Radiation Protection, University of Applied Sciences Gießen, Gießen 35390, Germany and Department of Radiotherapy and Radiation Oncology, University Medical Center Giessen and Marburg, Marburg 35043, Germany.
authors: Klemens
authors: K
authors: Zink
authors: Department of Biophysics, GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt 64291, Germany and Department of Condensed Matter Physics, Darmstadt University of Technology, Darmstadt 64289, Germany.
authors: Marco
authors: M
authors: Durante
authors: Medical Faculty of Philipps-University Marburg, Marburg 35032, Germany and Department of Radiotherapy and Radiation Oncology, University Medical Center Giessen and Marburg, Marburg 35043, Germany.
authors: Rita
authors: R
authors: Engenhart-Cabillic
authors: Department of Biophysics, GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt 64291, Germany.
authors: Michael
authors: M
authors: Scholz
mesh_terms: D002817:Chordoma / Q000532:radiotherapy; D063193:Heavy Ion Radiotherapy / Q000009:adverse effects / Q000379:methods*; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D058958:Organs at Risk / Q000528:radiation effects; D011874:Radiometry; D011880:Radiotherapy Planning, Computer-Assisted; D012062:Relative Biological Effectiveness; D012984:Software