title: Improvement of spread-out Bragg peak flatness for a carbon-ion beam by the use of a ridge filter with a ripple filter.
abstract: We have developed a novel design method of ridge filters for carbon-ion therapy using a broad-beam delivery system to improve the flatness of a biologically effective dose in the spread-out Bragg peak (SOBP). So far, the flatness of the SOBP is limited to about ±5% for carbon beams since the weight control of component Bragg curves composing the SOBP is difficult. This difficulty arises from using a large number of ridge-bar steps (e.g. about 100 for a SOBP width of 60 mm) required to form the SOBP for the pristine Bragg curve with an extremely sharp distal falloff. Instead of using a single ridge filter, we introduce a ripple filter to broaden the Bragg peak so that the number of ridge-bar steps can be reduced to about 30 for SOBP with of 60 mm for the ridge filter designed for the broadened Bragg peak. Thus we can manufacture the ridge filter more accurately and then attain a better flatness of the SOBP due to well-controlled weights of the component Bragg curves. We placed the ripple filter on the same frame of the ridge filter and arranged the direction of the ripple-filter-bar array perpendicular to that of the ridge-filter-bar array. We applied this method to a 290 MeV u(-1) carbon-ion beam in Heavy Ion Medical Accelerator in Chiba and verified the effectiveness by measurements.
authors.affiliation: Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8573, Japan.
authors.forename: Yousuke
authors.initials: Y
authors.lastname: Hara
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Takada
authors.forename: Kenji
authors.initials: K
authors.lastname: Hotta
authors.forename: Ryohei
authors.initials: R
authors.lastname: Tansho
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Nihei
authors.forename: Yojiro
authors.initials: Y
authors.lastname: Suzuki
authors.forename: Kosuke
authors.initials: K
authors.lastname: Nagafuchi
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Kawai
authors.forename: Masaki
authors.initials: M
authors.lastname: Tanabe
authors.forename: Shohei
authors.initials: S
authors.lastname: Mizutani
authors.forename: Takeshi
authors.initials: T
authors.lastname: Himukai
authors.forename: Naruhiro
authors.initials: N
authors.lastname: Matsufuji
mesh_terms: D055592:Biophysical Phenomena; D002244:Carbon / Q000627:therapeutic use*; D004867:Equipment Design; D005374:Filtration / Q000295:instrumentation; D063193:Heavy Ion Radiotherapy; D006801:Humans; D011882:Radiotherapy, High-Energy / Q000295:instrumentation / Q000706:statistics & numerical data; D012062:Relative Biological Effectiveness
chemical_list: D002244:Carbon