title: Applications of the microdosimetric function implemented in the macroscopic particle transport simulation code PHITS.
abstract: OBJECTIVE
  Microdosimetric quantities such as lineal energy are generally considered to be better indices than linear energy transfer (LET) for expressing the relative biological effectiveness (RBE) of high charge and energy particles. To calculate their probability densities (PD) in macroscopic matter, it is necessary to integrate microdosimetric tools such as track-structure simulation codes with macroscopic particle transport simulation codes.
  
  
  METHODS
  As an integration approach, the mathematical model for calculating the PD of microdosimetric quantities developed based on track-structure simulations was incorporated into the macroscopic particle transport simulation code PHITS (Particle and Heavy Ion Transport code System). The improved PHITS enables the PD in macroscopic matter to be calculated within a reasonable computation time, while taking their stochastic nature into account.
  
  
  CONCLUSIONS
  The microdosimetric function of PHITS was applied to biological dose estimation for charged-particle therapy and risk estimation for astronauts. The former application was performed in combination with the microdosimetric kinetic model, while the latter employed the radiation quality factor expressed as a function of lineal energy.
  
  
  CONCLUSIONS
  Owing to the unique features of the microdosimetric function, the improved PHITS has the potential to establish more sophisticated systems for radiological protection in space as well as for the treatment planning of charged-particle therapy.
authors.affiliation: Japan Atomic Energy Agency, Japan. sato.tatsuhiko@jaea.go.jp
authors.forename: Tatsuhiko
authors.initials: T
authors.lastname: Sato
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Watanabe
authors.forename: Lembit
authors.initials: L
authors.lastname: Sihver
authors.forename: Koji
authors.initials: K
authors.lastname: Niita
mesh_terms: D002470:Cell Survival / Q000528:radiation effects; D003359:Cosmic Radiation / Q000009:adverse effects; D020450:Heavy Ions / Q000009:adverse effects*; D006801:Humans; D055616:Microtechnology / Q000379:methods*; D008954:Models, Biological; D011874:Radiometry / Q000379:methods*