Mancusi Davide, Sihver Lembit, Niita Koji, Li Qiang, Sato Tatsuhiko, Iwase Hiroshi, Iwamoto Yosuke, Matsuda Norihiro, Sakamoto Yukio, Nakashima Hiroshi
Nuclear Engineering, Applied Physics, Chalmers University of Technology, Göteborg, Sweden.
Radiat Environ Biophys. 2009 Apr;48(2):135-43. doi: 10.1007/s00411-008-0206-8. Epub 2008 Dec 12.
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.
在近期用于外部癌症放射治疗的备选束流中，碳-9（(^9C)）受到了一定关注，因为预计在离子停止位置发生的两次α粒子和一个质子的β延迟发射会增强其生物效应。已开展实验对这种奇特束流进行物理特性表征，并开发了模型来定量估计其生物效应。在此，使用粒子与重离子输运代码系统（PHITS）计算碳-9束流在水中的能量沉积和线能量转移分布，并将结果与已发表的数据进行比较。尽管PHITS未能重现分布的某些特征，但它表明碳-9的衰变对能量沉积分布的贡献可忽略不计，这与之前对测量数据的解释相矛盾。我们还进行了微剂量学计算以估计衰变的生物效应，结果发现其可忽略不计；之前的微剂量学蒙特卡罗计算被发现是不正确的。一个几何性质的解析论证证实了这一结论，并给出了衰变额外生物效应的理论上限。然而，目前对于碳-9和碳-12之间观察到的生物效应差异尚无解释；这一惊人结果的可重复性将在未来实验中得到验证。
