title: Measurement of neutron ambient dose equivalent in passive carbon-ion and proton radiotherapies.
abstract: Secondary neutron ambient dose equivalents per the treatment absorbed dose in passive carbon-ion and proton radiotherapies were measured using a rem meter, WENDI-II at two carbon-ion radiotherapy facilities and four proton radiotherapy facilities in Japan. Our measured results showed that (1) neutron ambient dose equivalent in carbon-ion radiotherapy is lower than that in proton radiotherapy, and (2) the difference to the measured neutron ambient dose equivalents among the facilities is within a factor of 3 depending on the operational beam setting used at the facility and the arrangement of the beam line, regardless of the method for making a laterally uniform irradiation field: the double scattering method or the single-ring wobbling method. The reoptimization of the beam line in passive particle radiotherapy is an effective way to reduce the risk of secondary cancer because installing an adjustable precollimator and designing the beam line devices with consideration of their material, thickness and location, etc., can significantly reduce the neutron exposure. It was also found that the neutron ambient dose equivalent in passive particle radiotherapy is equal to or less than that in the photon radiotherapy. This result means that not only scanning particle radiotherapy but also passive particle radiotherapy can provide reduced exposure to normal tissues around the target volume without an accompanied increase in total body dose.
authors.affiliation: National Institute of Radiological Sciences, 4-9-1, Anagawa, Inage-ku, Chiba, 263-8555, Japan. yonai@nirs.go.jp
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Yonai
authors.forename: Naruhiro
authors.initials: N
authors.lastname: Matsufuji
authors.forename: Tatsuaki
authors.initials: T
authors.lastname: Kanai
authors.forename: Yuki
authors.initials: Y
authors.lastname: Matsui
authors.forename: Kaoru
authors.initials: K
authors.lastname: Matsushita
authors.forename: Haruo
authors.initials: H
authors.lastname: Yamashita
authors.forename: Masumi
authors.initials: M
authors.lastname: Numano
authors.forename: Takeji
authors.initials: T
authors.lastname: Sakae
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Terunuma
authors.forename: Teiji
authors.initials: T
authors.lastname: Nishio
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Kohno
authors.forename: Takashi
authors.initials: T
authors.lastname: Akagi
mesh_terms: D002244:Carbon / Q000627:therapeutic use*; D009502:Neutrons; D061766:Proton Therapy; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage
chemical_list: D002244:Carbon