[Development of in-house software for calculating and searching the restricted mass collision stopping powers for...

In external radiotherapy, the absorbed doses are measured using an ionization process in a gas-filled ionization chamber and estimated by the extended cavity theory. The calculation requires both the W-value of cavity gas and the restricted mass collision stopping powers (L/ρ) for the gas and medium. ICRU Report 37 gives us the data regarding the mass collision stopping powers (S/ρ) for several elements and chemical compounds or mixtures. However, there are no detailed data for L/ρ. In this study, we developed an in-house program to calculate the L/ρ for arbitrary substances by the use of the equation described in ICRU Report 37. With this program, we can search the calculated L/ρ easily. When we calculated L/ρ for chemical compounds and mixtures with implementation of Bragg's additivity rule, a large error of density effect corrections was observed. Therefore, our program adopted both the mean excitation energy and density effect correction obtained by ESTAR, which was developed by Berger et al. With adoption of these values, the calculation accuracy of our program was improved. Our program is useful to search L/ρ for radiation dosimetry in radiotherapy.