title: Calculation of energy-deposition distributions and microdosimetric estimation of the biological effect of a 9C beam.
abstract: Among the alternative beams being recently considered for external cancer radiotherapy, (9)C has received some attention because it is expected that its biological effectiveness could be boosted by the beta-delayed emission of two alpha particles and a proton that takes place at the ion-stopping site. Experiments have been performed to characterise this exotic beam physically and models have been developed to estimate quantitatively its biological effect. Here, the particle and heavy-ion transport code system ( PHITS ) is used to calculate energy-deposition and linear energy transfer distributions for a (9)C beam in water and the results are compared with published data. Although PHITS fails to reproduce some of the features of the distributions, it suggests that the decay of (9)C contributes negligibly to the energy-deposition distributions, thus contradicting the previous interpretation of the measured data. We have also performed a microdosimetric calculation to estimate the biological effect of the decay, which was found to be negligible; previous microdosimetric Monte-Carlo calculations were found to be incorrect. An analytical argument, of geometrical nature, confirms this conclusion and gives a theoretical upper bound on the additional biological effectiveness of the decay. However, no explanation can be offered at present for the observed difference in the biological effectiveness between (9)C and (12)C; the reproducibility of this surprising result will be verified in coming experiments.
authors.affiliation: Nuclear Engineering, Applied Physics, Chalmers University of Technology, Göteborg, Sweden. d.mancusi@ulg.ac.be
authors.forename: Davide
authors.initials: D
authors.lastname: Mancusi
authors.forename: Lembit
authors.initials: L
authors.lastname: Sihver
authors.forename: Koji
authors.initials: K
authors.lastname: Niita
authors.forename: Qiang
authors.initials: Q
authors.lastname: Li
authors.forename: Tatsuhiko
authors.initials: T
authors.lastname: Sato
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Iwase
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Iwamoto
authors.forename: Norihiro
authors.initials: N
authors.lastname: Matsuda
authors.forename: Yukio
authors.initials: Y
authors.lastname: Sakamoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakashima
mesh_terms: D000465:Algorithms; D001610:Beta Particles / Q000627:therapeutic use*; D002250:Carbon Radioisotopes / Q000627:therapeutic use*; D003198:Computer Simulation; D063193:Heavy Ion Radiotherapy; D006801:Humans; D018499:Linear Energy Transfer; D015233:Models, Statistical; D009010:Monte Carlo Method; D009369:Neoplasms / Q000532:radiotherapy*; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods*; D011878:Radiotherapy / Q000295:instrumentation* / Q000379:methods*; D012062:Relative Biological Effectiveness; D014867:Water
chemical_list: D002250:Carbon Radioisotopes; D014867:Water