title: Variation in patient position and impact on carbon-ion scanning beam distribution during prostate treatment.
abstract: OBJECTIVE
  We assessed the impact of changes in patient position on carbon-ion scanning beam distribution during treatment for prostate cancer.
  
  
  METHODS
  68 patients were selected. Carbon-ion scanning dose was calculated. Two different planning target volumes (PTVs) were defined: PTV1 was the clinical target volume plus a set-up margin for the anterior/lateral sides and posterior side, while PTV2 was the same as PTV1 minus the posterior side. Total prescribed doses of 34.4 Gy [relative biological effectiveness (RBE)] and 17.2 Gy (RBE) were given to PTV1 and PTV2, respectively. To estimate the influence of geometric variations on dose distribution, the dose was recalculated on the rigidly shifted single planning CT based on two dimensional-three dimensional rigid registration of the orthogonal radiographs before and after treatment for the fraction of maximum positional changes.
  
  
  RESULTS
  Intrafractional patient positional change values averaged over all patients throughout the treatment course were less than the target registration error = 2.00 mm and angular error = 1.27°. However, these maximum positional errors did not occur in all 12 treatment fractions. Even though large positional changes occurred during irradiation in all treatment fractions, lowest dose encompassing 95% of the target (D95)-PTV1 was >98% of the prescribed dose.
  
  
  CONCLUSIONS
  Intrafractional patient positional changes occurred during treatment beam irradiation and degraded carbon-ion beam dose distribution. Our evaluation did not consider non-rigid deformations, however, dose distribution was still within clinically acceptable levels.
  
  
  CONCLUSIONS
  Inter- and intrafractional changes did not affect carbon-ion beam prostate treatment accuracy.
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Mori
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Inaniwa
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Miki
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Tanimoto
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Tajiri
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: D
authors.initials: D
authors.lastname: Kuroiwa
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Nakao
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Shiraishi
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Shibayama
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Tsuji
mesh_terms: D063193:Heavy Ion Radiotherapy / Q000379:methods*; D006801:Humans; D008297:Male; D056888:Patient Positioning; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed