Accidental neutron exposure in a medical setting: a case study

Area of Science:

• Medical Physics
• Radiation Oncology
• Health Physics

Background:

• A new linear accelerator (Linac) was installed in a hospital oncology department in May 2016.
• Radiation shielding effectiveness is critical for patient and staff safety during Linac operation.

Purpose of the Study:

• To assess the adequacy of radiation shielding for a newly installed 18 MV linear accelerator.
• To evaluate radiation dose rates and compare them with regulatory limits and background levels.
• To validate biological dosimetry and Monte Carlo simulations in assessing occupational exposure.

Main Methods:

• Formal measurements of gamma and neutron dose rates by the Turkish Atomic Energy Authority.
• Biological dosimetry for personnel involved in the installation.
• Monte Carlo simulations to estimate tolerance dose ranges.
• Comparison of measured doses with simulated doses and background levels.

Main Results:

• Maximum neutron dose rate of 172 μSv h⁻¹ and gamma dose rate of 2 μSv h⁻¹ were recorded at 18 MV.
• Measured neutron dose rates significantly exceeded expected levels and local background.
• Biological dosimetry results aligned with neutron dosemeter readings and Monte Carlo simulations.
• Shielding was deemed insufficient, potentially due to inadequate design, necessitating photo-neutron mitigation strategies.

Conclusions:

• The shielding of the new Linac facility was inadequate, particularly concerning neutron radiation.
• Biological dosimetry and Monte Carlo simulations are valuable tools for assessing occupational exposure in complex scenarios.
• Careful planning and post-installation verification are essential for new radiation facilities, especially high MV Linacs, to manage photo-neutron production.