title: Influence of nuclear interactions in polyethylene range compensators for carbon-ion radiotherapy.
abstract: OBJECTIVE
  A recent study revealed that polyethylene (PE) would cause extra carbon-ion attenuation per range shift by 0.45%/cm due to compositional differences in nuclear interactions. The present study aims to assess the influence of PE range compensators on tumor dose in carbon-ion radiotherapy.
  
  
  METHODS
  Carbon-ion radiation was modeled to be composed of primary carbon ions and secondary particles, for each of which the dose and the relative biological effectiveness (RBE) were estimated at a tumor depth in the middle of spread-out Bragg peak. Assuming exponential behavior for attenuation and yield of these components with depth, the PE effect on dose was calculated for clinical carbon-ion beams and was partly tested by experiment. The two-component model was integrated into a treatment-planning system and the PE effect was estimated in two clinical cases.
  
  
  RESULTS
  The attenuation per range shift by PE was 0.1%-0.3%/cm in dose and 0.2%-0.4%/cm in RBE-weighted dose, depending on energy and range-modulation width. This translates into reduction of RBE-weighted dose by up to 3% in extreme cases. In the treatment-planning study, however, the effect on RBE-weighted dose to tumor was typically within 1% reduction.
  
  
  CONCLUSIONS
  The extra attenuation of primary carbon ions in PE was partly compensated by increased secondary particles for tumor dose. In practical situations, the PE range compensators would normally cause only marginal errors as compared to intrinsic uncertainties in treatment planning, patient setup, beam delivery, and clinical response.
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Kanematsu
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Koba
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
authors.forename: Risa
authors.initials: R
authors.lastname: Ogata
authors.affiliation: Ion Beam Therapy Center, SAGA HIMAT Foundation, 415 Harakoga-machi, Tosu, Saga 841-0071, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Himukai
mesh_terms: D000465:Algorithms; D002244:Carbon / Q000627:therapeutic use*; D002817:Chordoma / Q000000981:diagnostic imaging / Q000532:radiotherapy; D003198:Computer Simulation; D006801:Humans; D007477:Ions / Q000627:therapeutic use*; D008545:Melanoma / Q000000981:diagnostic imaging / Q000532:radiotherapy; D008962:Models, Theoretical; D009369:Neoplasms / Q000532:radiotherapy; D009669:Nose Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D020959:Polyethylene / Q000737:chemistry*; D011835:Radiation Protection / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012447:Sacrum / Q000000981:diagnostic imaging; D013125:Spinal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D014057:Tomography, X-Ray Computed
chemical_list: D007477:Ions; D002244:Carbon; D020959:Polyethylene