Angular dependence ofH_p(3): horizontal vs. vertical rotation

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Radiological Protection

Background:

• Operational quantities like H_p(3) are crucial for radiation protection.
• Standard measurement protocols often assume vertical rotation of phantoms.
• Investigating phantom rotation effects is vital for accurate dose assessment.

Purpose of the Study:

• To compare H_p(3) values using horizontal versus vertical phantom rotation under oblique incidence.
• To evaluate the impact of rotation axis on photon and beta radiation dosimetry.
• To assess the implications for eye lens dose (H_lens) calculations.

Main Methods:

• Calculated conversion coefficients (h_pK(3) and h_pD(3)) for photons and betas.
• Simulated mono-energetic photons (2 keV–10 MeV) and reference beta fields.
• Determined ratios of H_p(3) for horizontal and vertical rotations.
• Calculated and compared H_lens ratios.

Main Results:

• Horizontal rotation significantly reduces H_p(3) for photons, especially at low energies and high incidence angles.
• Beta particle H_p(3) differences between rotations are generally below 10%.
• H_lens shows larger differences than H_p(3) for both photons and betas.

Conclusions:

• Phantom rotation axis critically affects H_p(3) for photons, necessitating consideration of horizontal rotation.
• Current dosimetry protocols may require updates for accurate dose assessment, particularly for eye lens.
• Findings inform the International Commission on Radiation Units and Measurements (ICRU) regarding H_p(3) definition and International Standardization Organization (ISO) and International Electrotechnical Commission (IEC) testing procedures.