A new dose determination method for H_p(3) and d_{P LENS} for beta reference radiation qualities

For the purpose of obtaining the smaller uncertainties for H_p(3) and D_{p lens} in ⁹⁰Sr/⁹⁰Y beta reference fields, a new dose determination method based on the Monte-Carlo simulation was proposed. The conversion coefficients from the absorbed dose in air, at the reference point of the extrapolation ionisation chamber, D_air,det to H_p(3; α) and the conversion factors from D_air,det to D_{p lens}(α) were calculated with EGSnrc, respectively, for the irradiation angles from 0 deg. to 60 deg. Compared with the dose determination method in International Organization for Standardization (ISO) 6980 standard, the uncertainty reductions of 7.7-52.8% for H_p(3; α) and 7.9-55.0% for D_{p lens}(α) were achieved, respectively. In addition, for the conversion coefficients from the reference absorbed dose D_R to H_p(3; α), the calculations were performed for more irradiation conditions, which are not included in the current ISO 6980 standard. For the calculations of the conversion factors from D_R to D_{p lens}(α), the eye and head phantoms with Chinese characteristics were utilised, which makes the conversion factors more suitable for use in China. (authors)