Neutron dose from a 6-MV X-ray beam in radiotherapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Nuclear Physics

Background:

• Clinical use of 6-MV X-ray beams as non-neutron-producing beams.
• Lack of quantitative data on neutron production from 6-MV beams.
• Importance of understanding neutron dose for radiotherapy safety and risk assessment.

Purpose of the Study:

• To theoretically deduce neutron dose from 6-MV X-ray beams.
• To assess the safety and risk associated with neutron production in radiotherapy.
• To compare neutron production between 6-MV and 10-MV beams.

Main Methods:

• Utilized Monte Carlo simulations for neutron dose calculation.
• Surveyed nuclear database for nuclei with neutron separation energies below 6 MeV.
• Performed calculations considering deuterium (²H) in a phantom and other elements like tungsten-183 (¹⁸³W).

Main Results:

• Identified two components of neutron dose: one from ²H within the irradiation field, and another from elements like ¹⁸³W spreading from the gantry.
• Calculated neutron doses at 0 and 50 cm from the irradiation field as 27 and 1.5 nSv/MU, respectively, for intensity-modulated radiotherapy (IMRT) or volumetric modulated arc therapy (VMAT).
• Estimated 6-MV beams to be approximately 70 times safer than 10-MV beams for IMRT/VMAT and 20 times safer for total body irradiation.

Conclusions:

• The study provides the first theoretical quantification of neutron dose from 6-MV X-ray beams.
• Neutron doses from 6-MV beams are significantly lower compared to 10-MV beams, indicating enhanced safety.
• Findings contribute to improved safety protocols and risk management in radiation therapy.