Estimation of clinical dose by a tissue equivalent proportional counter for heavy-ion radiotherapy

In high energy heavy-ion radiotherapy, a clinical dose is so important index as the absorbed dose; the clinical dose was specially defined as the absorbed dose for 60Co gamma-ray corresponding to the same survival fraction for radiation of interest. In this work, the energy deposit spectra for carbon-ion beam (Carbon 290 MeV/nucleon, 60 mm spread-out Bragg peak (SOBP)) which have been clinically used were measured with a tissue equivalent proportional counter (TEPC) at various depth in the target volume. Then the clinical dose was estimated from the measured spectra by means of dual radiation action model. It was found that if the absorbed dose and linear quadratic (LQ) model parameter, α and β, were normalized, then the estimated clinical depth dose distribution agreed with the calculation based on cell survival fraction of human salivary grand (HSG) tumor cell lines. (author)