Transitioning from Gamma Rays to X Rays for Comparable Biomedical Research Irradiations: Energy Matters

Area of Science:

• Biomedical research
• Radiation biology
• Medical physics

Background:

• Radiation dose standardization is crucial for reproducible biological data.
• Security measures have increased for radioactive isotopes, prompting a shift to kilovoltage X-ray irradiators.
• Kilovoltage X-ray irradiators have variable energies, affecting radiation interactions.

Purpose of the Study:

• To highlight challenges in standardizing radiation doses using kilovoltage X-ray irradiators for biological research.
• To explain the dosimetric differences between X-rays and gamma rays, particularly concerning bone marrow exposure.
• To discuss implications for hematopoietic cell sensitivity and data comparability.

Main Methods:

• Analysis of radiation interactions (Compton scattering, photoelectric effect) at different X-ray energies.
• Comparison of dose distribution in bone and bone marrow for X-ray and gamma-ray sources.
• Evaluation of the impact of energy-dependent dose variations on biological outcomes.

Main Results:

• The photoelectric effect predominates in low-energy X-ray irradiators, leading to higher doses in bony tissues and bone marrow.
• Average radiation absorbed dose to mouse bone marrow can increase by up to 30% with kilovoltage X-rays.
• Steep dose gradients and qualitatively different outcomes complicate biological dose equivalency adjustments.

Conclusions:

• Shifting to kilovoltage X-ray irradiators requires careful consideration of increased bone marrow dose and altered radiation effects.
• Implementing higher beam energies and acknowledging differences from gamma-ray data are essential for accurate research.
• Ensuring accurate radiation dose standardization is critical for reproducible and comparable biological research outcomes.