title: A patient-specific aperture system with an energy absorber for spot scanning proton beams: Verification for clinical application.
abstract: OBJECTIVE
  In the authors' proton therapy system, the patient-specific aperture can be attached to the nozzle of spot scanning beams to shape an irradiation field and reduce lateral fall-off. The authors herein verified this system for clinical application.
  
  
  METHODS
  The authors prepared four types of patient-specific aperture systems equipped with an energy absorber to irradiate shallow regions less than 4 g/cm(2). The aperture was made of 3-cm-thick brass and the maximum water equivalent penetration to be used with this system was estimated to be 15 g/cm(2). The authors measured in-air lateral profiles at the isocenter plane and integral depth doses with the energy absorber. All input data were obtained by the Monte Carlo calculation, and its parameters were tuned to reproduce measurements. The fluence of single spots in water was modeled as a triple Gaussian function and the dose distribution was calculated using a fluence dose model. The authors compared in-air and in-water lateral profiles and depth doses between calculations and measurements for various apertures of square, half, and U-shaped fields. The absolute doses and dose distributions with the aperture were then validated by patient-specific quality assurance. Measured data were obtained by various chambers and a 2D ion chamber detector array.
  
  
  RESULTS
  The patient-specific aperture reduced the penumbra from 30% to 70%, for example, from 34.0 to 23.6 mm and 18.8 to 5.6 mm. The calculated field width for square-shaped apertures agreed with measurements within 1 mm. Regarding patient-specific aperture plans, calculated and measured doses agreed within -0.06% ± 0.63% (mean ± SD) and 97.1% points passed the 2%-dose/2 mm-distance criteria of the γ-index on average.
  
  
  CONCLUSIONS
  The patient-specific aperture system improved dose distributions, particularly in shallow-region plans.
authors.affiliation: Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya-shi, Aichi-ken 462-8508, Japan and Department of Radiological Sciences, Nagoya University Graduate School of Medicine, 1-1-20, Daikouminami, Higashi-ku, Nagoya-shi, Aichi-ken 461-8673, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Yasui
authors.affiliation: Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya-shi, Aichi-ken 462-8508, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Toshito
authors.affiliation: Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya-shi, Aichi-ken 462-8508, Japan.
authors.forename: Chihiro
authors.initials: C
authors.lastname: Omachi
authors.affiliation: Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya-shi, Aichi-ken 462-8508, Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Kibe
authors.affiliation: Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya-shi, Aichi-ken 462-8508, Japan.
authors.forename: Kensuke
authors.initials: K
authors.lastname: Hayashi
authors.affiliation: Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya-shi, Aichi-ken 462-8508, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Shibata
authors.affiliation: Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya-shi, Aichi-ken 462-8508, Japan.
authors.forename: Kenichiro
authors.initials: K
authors.lastname: Tanaka
authors.affiliation: Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya-shi, Aichi-ken 462-8508, Japan.
authors.forename: Eiki
authors.initials: E
authors.lastname: Nikawa
authors.affiliation: Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya-shi, Aichi-ken 462-8508, Japan.
authors.forename: Kumiko
authors.initials: K
authors.lastname: Asai
authors.affiliation: Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya-shi, Aichi-ken 462-8508, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Shimomura
authors.affiliation: Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya-shi, Aichi-ken 462-8508, Japan.
authors.forename: Hideto
authors.initials: H
authors.lastname: Kinou
authors.affiliation: Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya-shi, Aichi-ken 462-8508, Japan.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Isoyama
authors.affiliation: Hitachi, Ltd., Hitachi Research Laboratory, 7-1-1, Omika-chou, Hitachi-shi, Ibaraki-ken 319-1292, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Fujii
authors.affiliation: Hitachi, Ltd., Hitachi Research Laboratory, 7-1-1, Omika-chou, Hitachi-shi, Ibaraki-ken 319-1292, Japan.
authors.forename: Taisuke
authors.initials: T
authors.lastname: Takayanagi
authors.affiliation: Hitachi, Ltd., Hitachi Research Laboratory, 7-1-1, Omika-chou, Hitachi-shi, Ibaraki-ken 319-1292, Japan.
authors.forename: Shusuke
authors.initials: S
authors.lastname: Hirayama
authors.affiliation: Hitachi, Ltd., Hitachi Works, 3-1-1, Saiwai-chou, Hitachi-shi, Ibaraki-ken 317-8511, Japan.
authors.forename: Yoshihiko
authors.initials: Y
authors.lastname: Nagamine
authors.affiliation: Graduate School of Medical Sciences, Nagoya City University, 1, Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya-shi, Aichi-ken 467-8601, Japan.
authors.forename: Yuta
authors.initials: Y
authors.lastname: Shibamoto
authors.affiliation: Department of Radiological Sciences, Nagoya University Graduate School of Medicine, 1-1-20, Daikouminami, Higashi-ku, Nagoya-shi, Aichi-ken 461-8673, Japan.
authors.forename: Masataka
authors.initials: M
authors.lastname: Komori
authors.affiliation: Nagoya Proton Therapy Center, Nagoya City West Medical Center, 1-1-1, Hirate-cho, Kita-ku, Nagoya-shi, Aichi-ken 462-8508, Japan.
authors.forename: Jun-etsu
authors.initials: JE
authors.lastname: Mizoe
mesh_terms: D000388:Air; D004867:Equipment Design; D006801:Humans; D009010:Monte Carlo Method; D057285:Precision Medicine / Q000295:instrumentation* / Q000379:methods; D061766:Proton Therapy / Q000295:instrumentation* / Q000379:methods; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D014867:Water
chemical_list: D014867:Water