title: Field-size dependence of doses of therapeutic carbon beams.
abstract: To estimate the physical dose at the center of spread-out Bragg peaks (SOBP) for various conditions of the irradiation system, a semiempirical approach was applied. The dose at the center of the SOBP depends on the field size because of large-angle scattering particles in the water phantom. For a small field of 5 x 5 cm2, the dose was reduced to 99.2%, 97.5%, and 96.5% of the dose used for the open field in the case of 290, 350, and 400 MeV/n carbon beams, respectively. Based on the three-Gaussian form of the lateral dose distributions of the carbon pencil beam, which has previously been shown to be effective for describing scattered carbon beams, we reconstructed the dose distributions of the SOBP beam. The reconstructed lateral dose distribution reproduced the measured lateral dose distributions very well. The field-size dependencies calculated using the reconstructed lateral dose distribution of the therapeutic carbon beam agreed with the measured dose dependency very well. The reconstructed beam was also used for irregularly shaped fields. The resultant dose distribution agreed with the measured dose distribution. The reconstructed beams were found to be applicable to the treatment-planning system.
authors.affiliation: Tokai University Unified Graduate School, Graduate School of Science and Technology, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1207, Japan.
authors.forename: Yohsuke
authors.initials: Y
authors.lastname: Kusano
authors.forename: Tatsuaki
authors.initials: T
authors.lastname: Kanai
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Yonai
authors.forename: Masataka
authors.initials: M
authors.lastname: Komori
authors.forename: Noritoshi
authors.initials: N
authors.lastname: Ikeda
authors.forename: Yuji
authors.initials: Y
authors.lastname: Tachikawa
authors.forename: Atsushi
authors.initials: A
authors.lastname: Ito
authors.forename: Hirohisa
authors.initials: H
authors.lastname: Uchida
mesh_terms: D002244:Carbon / Q000737:chemistry*; D063193:Heavy Ion Radiotherapy; D007477:Ions; D015233:Models, Statistical; D016011:Normal Distribution; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011882:Radiotherapy, High-Energy / Q000379:methods*; D012542:Scattering, Radiation; D014867:Water / Q000737:chemistry
chemical_list: D007477:Ions; D014867:Water; D002244:Carbon