title: Influence of nuclear interactions in body tissues on tumor dose in carbon-ion radiotherapy.
abstract: OBJECTIVE
  In carbon-ion radiotherapy treatment planning, the planar integrated dose (PID) measured in water is applied to the patient dose calculation with density scaling using the stopping power ratio. Since body tissues are chemically different from water, this dose calculation can be subject to errors, particularly due to differences in inelastic nuclear interactions. In recent studies, the authors proposed and validated a PID correction method for these errors. In the present study, the authors used this correction method to assess the influence of these nuclear interactions in body tissues on tumor dose in various clinical cases.
  
  
  METHODS
  Using 10-20 cases each of prostate, head and neck (HN), bone and soft tissue (BS), lung, liver, pancreas, and uterine neoplasms, the authors first used treatment plans for carbon-ion radiotherapy without nuclear interaction correction to derive uncorrected dose distributions. The authors then compared these distributions with recalculated distributions using the nuclear interaction correction (corrected dose distributions).
  
  
  RESULTS
  Median (25%/75% quartiles) differences between the target mean uncorrected doses and corrected doses were 0.2% (0.1%/0.2%), 0.0% (0.0%/0.0%), -0.3% (-0.4%/-0.2%), -0.1% (-0.2%/-0.1%), -0.1% (-0.2%/0.0%), -0.4% (-0.5%/-0.1%), and -0.3% (-0.4%/0.0%) for the prostate, HN, BS, lung, liver, pancreas, and uterine cases, respectively. The largest difference of -1.6% in target mean and -2.5% at maximum were observed in a uterine case.
  
  
  CONCLUSIONS
  For most clinical cases, dose calculation errors due to the water nonequivalence of the tissues in nuclear interactions would be marginal compared to intrinsic uncertainties in treatment planning, patient setup, beam delivery, and clinical response. In some extreme cases, however, these errors can be substantial. Accordingly, this correction method should be routinely applied to treatment planning in clinical practice.
authors.affiliation: Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage-ku, Chiba 263-8555, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Inaniwa
authors.affiliation: Medical Physics Research Program, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Anagawa 4-9-1, Inage-ku, Chiba 263-8555, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Kanematsu
authors.affiliation: Hospital, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Tsuji
authors.affiliation: Hospital, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Kamada
mesh_terms: D003198:Computer Simulation; D063193:Heavy Ion Radiotherapy / Q000379:methods*; D006801:Humans; D009369:Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism / Q000532:radiotherapy*; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed