title: Microdosimetric approach to NIRS-defined biological dose measurement for carbon-ion treatment beam.
abstract: The RBE-weighted absorbed dose, called "biological dose," has been routinely used for carbon-ion treatment planning in Japan to formulate dose prescriptions for treatment protocols. This paper presents a microdosimetric approach to measuring the biological dose, which was redefined to be derived from microdosimetric quantities measured by a tissue-equivalent proportional counter (TEPC). The TEPC was calibrated in (60)Co gamma rays to assure a traceability of the TEPC measurement to Japanese standards and to eliminate the discrepancies among matching counters. The absorbed doses measured by the TEPC were reasonably coincident with those measured by a reference ionization chamber. The RBE value was calculated from the microdosimetric spectrum on the basis of the microdosimetric kinetic model. The biological doses obtained by the TEPC were compared with those prescribed in the carbon-ion treatment planning system. We found that it was reasonable for the measured biological doses to decrease with depth around the rear SOBP region because of beam divergence, scattering effect, and fragmentation reaction. These results demonstrate that the TEPC can be an effective tool to assure the radiation quality in carbon-ion radiotherapy.
authors.affiliation: Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan. y.kase@scchr.jp
authors.forename: Yuki
authors.initials: Y
authors.lastname: Kase
authors.forename: Tatsuaki
authors.initials: T
authors.lastname: Kanai
authors.forename: Makoto
authors.initials: M
authors.lastname: Sakama
authors.forename: Yuji
authors.initials: Y
authors.lastname: Tameshige
authors.forename: Takeshi
authors.initials: T
authors.lastname: Himukai
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nose
authors.forename: Naruhiro
authors.initials: N
authors.lastname: Matsufuji
mesh_terms: D000465:Algorithms; D004867:Equipment Design; D019544:Equipment Failure Analysis; D063193:Heavy Ion Radiotherapy; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods*; D012062:Relative Biological Effectiveness; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity