Proposal for a new operational quantity to assess the effective dose in the event of external exposure to photons

Highlights: • The dose equivalent Hp(30)_water constitutes a good function of effective dose. • Fluence-to- Hp(30)_water conversion coefficients are calculated using. • The use of Hp(30)_water for individual monitoring overcomes most of the shortcomings. Despite its shortcomings and inconsistencies such as using the kerma approximation, the ICRU tissue, which does not really exist and the radiation quality factor Q defined in water, the personal dose equivalent Hp defined in the 1980s remains until now the operational quantity used to assess the effective dose E for external exposure. To help overcome most of these shortcomings and inconsistencies a new operational quantity Hp(30)_water to replace Hp(10) is proposed. Fluence-to Hp(30) _water conversion coefficients are calculated for photon energies from 0.02 to 10 MeV using the Monte Carlo transport code EGSnrc. Calculations are performed in a water cube phantom using full transport of secondary charged particles. The comparison of the conversion coefficients of Hp(30) and E shows that Hp(30) _water can represent a good envelope of E over the whole energy range considered.