Can heavy charged particles really be regarded as high-LET radiations with respect to their radiobiological actions? I: LETs and fluences of heavy charged particles and associated delta-rays.
The structures of the energy transfer of heavy charged particles (HCP) to nm-size targets have been investigated, taking account of delta-ray generation by HCP as well as associated delta-rays. From the microdosimetric viewpoint, the radiobiological effects of HCP have to be analysed in terms of the microdosimetric quantities based on the local energy transfer (LET) to the target, that is the restricted linear energy transfer (Ldelta), and the fluences or the degradation spectra of charged particles including delta-rays. Ldelta of HCP and delta-rays, and the fluences of delta-rays have been calculated for various HCP (H-Ar) with energies 1, 10 and 100 MeV amu(-1). From the results obtained, it is concluded that heavy ions (HI) should be expressed as two-component radiations which are composed of high-Ldelta heavy ion tracks of low fluence and low-Ldelta delta-rays of high fluence; in other words, the currently used expression 'HI are high-LET radiations' is not valid.
Iwanami
S
S
School of Allied Health Sciences, Kitasato University, Kanagawa, Japan. iwanami@medcc.kitasato-u.ac.jp
Oda
N
N
D007700:Kinetics; D018499:Linear Energy Transfer; D015233:Models, Statistical; D009683:Nuclear Medicine / Q000379:methods