High-LET dose-response characteristics described by track structure theory of heavy charged particles

The track structure theory developed by Katz and coworkers describes the effect of high-LET radiation to the highly inhomogeneous dose distribution due to low energy δ-rays ejected from the particle track. The theory predicts the effectiveness of high-LET radiation by using the ion parameters zeff effective charge of the ion, and β = v/c, the relative ion velocity, together with the characteristic dose D37 derived from low-LET dose-response characteristic of the detector and the approximate size a of the sensitive element of the detector. 60Co gamma-irradiation is used as a reference low-LET radiation, while high-LET radiation ranging from 16MeV protons to 4MeV/amu 16O-ions covering an initial LET range of 30-5500 MeVcm2/g is obtained from a tandem Van de Graff accelerator.  A thin film (5mg/cm2) radiochromic dye cyanide plastic dosemeter was used as detector with the characteristic dose of 16.8 Mrad and a sensitive element size of 10-7.

Theoretical and experimental effectiveness, RBE. agreed within 10 to 25% depending on LET.