title: Estimation of late rectal normal tissue complication probability parameters in carbon ion therapy for prostate cancer.
abstract: OBJECTIVE
  The aim of this study was to estimate normal tissue complication probability (NTCP) parameters for late rectal complications after carbon ion radiotherapy (C-ion RT) for prostate cancer.
  
  
  METHODS
  A total of 163 patients were used to derive NTCP parameters. These patients were treated with relative biological effectiveness (RBE)-weighted dose ranging from 57.6 Gy (RBE) up to 72 Gy (RBE) and included in dose escalation trials. The Lyman-Kutcher-Burman (LKB) model was used and the model parameters were fit to the relation between dose and complication observed after C-ion RT.
  
  
  RESULTS
  The resulting NTCP parameters were the volume effect parameter; n=0.035 (95% CI: 0.024-0.047), the steepness of the NTCP curve; m=0.10 (0.084-0.13), the tolerance dose associated with 50% probability of complication; TD50=63.6 Gy (RBE) (61.8-65.4 Gy (RBE)) for Grade⩾1, n=0.012 (0.0050-0.023), m=0.046 (0.033-0.062), TD50=69.1 Gy (RBE) (67.6-70.9 Gy (RBE)) for Grade⩾2.
  
  
  CONCLUSIONS
  A new set of rectal NTCP parameters in C-ion RT was determined. The rather small n values suggest that the rectum was consistent with being strictly serial organ. The new derived parameter values facilitate estimation of rectal NTCP in C-ion RT.
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Japan. Electronic address: fukahori@nirs.go.jp.
authors.forename: Mai
authors.initials: M
authors.lastname: Fukahori
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Japan.
authors.forename: Naruhiro
authors.initials: N
authors.lastname: Matsufuji
authors.affiliation: Ion-Beam Therapy Center, SAGA HIMAT Foundation, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Himukai
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Kanematsu
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Japan.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Mizuno
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Japan.
authors.forename: Akifumi
authors.initials: A
authors.lastname: Fukumura
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tsuji
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Japan.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Kamada
mesh_terms: D063193:Heavy Ion Radiotherapy / Q000009:adverse effects*; D006801:Humans; D008297:Male; D011336:Probability; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D012007:Rectum / Q000528:radiation effects*; D012062:Relative Biological Effectiveness
keywords: Carbon ion radiotherapy; NTCP; Prostate cancer