A NEW DOSE DETERMINATION METHOD FOR HP(3) AND DP LENS FOR BETA REFERENCE RADIATION QUALITIES.

For the purpose of obtaining the smaller uncertainties for Hp(3) and Dp 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, Dair, det to Hp(3; α) and the conversion factors from Dair, det to Dp lens(α) were calculated with EGSnrc, respectively, for the irradiation angles from 0° to 60°. Compared with the dose determination method in International Organization for Standardization (ISO) 6980 standard, the uncertainty reductions of 7.7-52.8% for Hp(3; α) and 7.9-55.0% for Dp lens(α) were achieved, respectively. In addition, for the conversion coefficients from the reference absorbed dose DR to Hp(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 DR to Dp lens(α), the eye and head phantoms with Chinese characteristics were utilised, which makes the conversion factors more suitable for use in China.

CALCULATION OF THE DOSE CONVERSION COEFFICIENTS FOR CHINESE EYE LENS UNDER PHOTON EXPOSURE.

In this work, the conversion coefficients from air kerma to the eye lens dose were calculated for photon exposures using the detailed eye and head Monte-Carlo (MC) model with the Chinese adult parameters. To verify the MC model and the simulation method, the conversion coefficients from fluence to the eye lens dose for mono-energy electrons (0.7-12 MeV) were calculated and compared with other studies. Then the conversion coefficients from air kerma to the doses in the entire lens and in the sensitive volume were calculated, respectively, for mono-energy photons (0.01-50 MeV) at different incidence angles (0-90°, in step of 15°). A small difference was found between the calculated conversion coefficient and the ICRP recommended value. The difference could be mainly due to the difference in their geometry characteristic of the eye and head models. In addition, the uncertainty analysis of the calculated conversion coefficients was performed in detail. The calculated dose conversion coefficient of the eye lens can be used to evaluate the eye lens dose for Chinese occupational staffs in external photon fields. And it can be used to determine the personal absorbed dose in the eye lens Dp lens in photon reference radiation fields.