title: Secondary neutron dose measurement for proton eye treatment using an eye snout with a borated neutron absorber.
abstract: BACKGROUND
  We measured and assessed ways to reduce the secondary neutron dose from a system for proton eye treatment.
  
  
  METHODS
  Proton beams of 60.30 MeV were delivered through an eye-treatment snout in passive scattering mode. Allyl diglycol carbonate (CR-39) etch detectors were used to measure the neutron dose in the external field at 0.00, 1.64, and 6.00 cm depths in a water phantom. Secondary neutron doses were measured and compared between those with and without a high-hydrogen-boron-containing block. In addition, the neutron energy and vertices distribution were obtained by using a Geant4 Monte Carlo simulation.
  
  
  RESULTS
  The ratio of the maximum neutron dose equivalent to the proton absorbed dose (H(10)/D) at 2.00 cm from the beam field edge was 8.79 ± 1.28 mSv/Gy. The ratio of the neutron dose equivalent to the proton absorbed dose with and without a high hydrogen-boron containing block was 0.63 ± 0.06 to 1.15 ± 0.13 mSv/Gy at 2.00 cm from the edge of the field at depths of 0.00, 1.64, and 6.00 cm.
  
  
  CONCLUSIONS
  We found that the out-of-field secondary neutron dose in proton eye treatment with an eye snout is relatively small, and it can be further reduced by installing a borated neutron absorbing material.
authors.affiliation: Department of Radiation Oncology, Kyung Hee University Hospital at Gandong, Seoul, Korea.
authors.forename: Dong Wook
authors.initials: DW
authors.lastname: Kim
authors.forename: Weon Kuu
authors.initials: WK
authors.lastname: Chung
authors.forename: Jungwook
authors.initials: J
authors.lastname: Shin
authors.forename: Young Kyung
authors.initials: YK
authors.lastname: Lim
authors.forename: Dongho
authors.initials: D
authors.lastname: Shin
authors.forename: Se Byeong
authors.initials: SB
authors.lastname: Lee
authors.forename: Myongguen
authors.initials: M
authors.lastname: Yoon
authors.forename: Sung-Yong
authors.initials: SY
authors.lastname: Park
authors.forename: Dong Oh
authors.initials: DO
authors.lastname: Shin
authors.forename: Jung Keun
authors.initials: JK
authors.lastname: Cho
mesh_terms: D005134:Eye Neoplasms / Q000532:radiotherapy; D006801:Humans; D009010:Monte Carlo Method; D009502:Neutrons; D061766:Proton Therapy / Q000295:instrumentation / Q000379:methods; D011874:Radiometry / Q000379:methods*