Calculation of effective doses for broad parallel photon beams

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Computational Physics

Background:

• Effective dose (E) is crucial for radiation protection and risk assessment.
• Accurate calculation of E requires considering various irradiation geometries.
• Existing dose equivalent (H(E)) values are often used as a proxy for E.

Purpose of the Study:

• To calculate effective dose (E) for broad parallel photon beams across all incident directions.
• To compare calculated E with dose equivalent (H(E)) values.
• To propose improvements for personal dosimeter angular response.

Main Methods:

• Utilized the Monte Carlo N-Particle (MCNP) transport code.
• Employed a hermaphroditic phantom for dose calculations.
• Analyzed conversion coefficients from air kerma to effective dose.

Main Results:

• Effective dose (E) was consistently found to be less than dose equivalent (H(E)) for all beam directions and energies.
• Differences between E and H(E) were generally insignificant, except for overhead and underfoot beam incidence.
• Proposed ideal angular response factors for personal dosimeters based on E and H(E) distributions.

Conclusions:

• Current H(E) values can be interpreted as E or a conservative estimate, simplifying dosimetry without detailed geometry.
• The findings support the use of H(E) in radiation protection, with awareness of specific directional exceptions.
• The proposed angular response factors can enhance the accuracy of personal dosimeters for diverse photon beam exposures.