title: Microdosimetric calculation of penumbra for biological dose in wobbled carbon-ion beams with Monte Carlo Method.
abstract: In carbon-ion radiotherapy, it is important to evaluate the biological dose because the relative biological effectiveness values vary greatly in a patient's body. The microdosimetric kinetic model (MKM) is a method of estimating the biological effect of radiation by use of microdosimetry. The lateral biological dose distributions were estimated with a modified MKM, in which we considered the overkilling effect in the high linear-energy-transfer region. In this study, we used the Monte Carlo calculation of the Geant4 code to simulate a horizontal port at the Heavy Ion Medical Accelerator in Chiba of the National Institute of Radiological Sciences. The lateral biological dose distributions calculated by Geant4 were almost flat as the lateral absorbed dose in the flattened area. However, in the penumbra region, the lateral biological dose distributions were sharper than the lateral absorbed dose distributions. Furthermore, the differences between the lateral absorbed dose and biological dose distributions were dependent on the depth for each multi-leaf collimator opening size. We expect that the lateral biological dose distribution presented here will enable high-precision calculations for a treatment-planning system.
authors.affiliation: Department of Radiological Sciences, Graduate School of Medicine, Nagoya University, 1-1-20 Daiko-Minami, Higashi-ku, Nagoya, Aichi, Japan. tamura.mikoto@a.nagoya-u.jp
authors.forename: Mikoto
authors.initials: M
authors.lastname: Tamura
authors.forename: Masataka
authors.initials: M
authors.lastname: Komori
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Oguchi
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Iwamoto
authors.forename: Toshiya
authors.initials: T
authors.lastname: Rachi
authors.forename: Kenji
authors.initials: K
authors.lastname: Ota
authors.forename: Atsushi
authors.initials: A
authors.lastname: Hemmi
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Shimozato
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Obata
mesh_terms: D002244:Carbon / Q000627:therapeutic use*; D002540:Cerebral Cortex / Q000528:radiation effects*; D003198:Computer Simulation; D063193:Heavy Ion Radiotherapy; D006801:Humans; D007700:Kinetics; D008962:Models, Theoretical; D009010:Monte Carlo Method; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012062:Relative Biological Effectiveness
chemical_list: D002244:Carbon