Photon and Neutron Dose Estimation Using Monte Carlo Simulation in TrueBeam's Room

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiation Detection and Measurement

Background:

• High-energy photon beams in radiation therapy can generate secondary neutrons.
• Accurate assessment of neutron ambient dose equivalent is crucial for radiation safety in the vicinity of medical linear accelerators.

Purpose of the Study:

• To investigate the distribution of neutron ambient dose equivalent within the TrueBeam 10 MV photon chamber.
• To compare simulated neutron dose equivalents with measured values for different field sizes.

Main Methods:

• Simulations were performed using the Particle and Heavy Ion Transport Code System (PHITS) and JENDL-5.0.
• Neutron ambient dose equivalent was measured using CR-39 detectors.
• Comparisons were made for 10 MV photon beams with field sizes of 20 cm x 20 cm and 0.5 cm x 0.5 cm, at 5000 monitor units.

Main Results:

• Neutron ambient dose equivalents for the 0.5 cm x 0.5 cm field size were 4% to 30% higher than those for the 20 cm x 20 cm field size, particularly out of the primary beam field.
• The differences between simulated and measured neutron ambient dose equivalents were less than 20% at all measured points.

Conclusions:

• The PHITS and JENDL-5.0 simulation accurately predicted neutron ambient dose equivalents.
• The simulation results are in good agreement with experimental measurements, validating the methodology for assessing neutron dose in TrueBeam photon therapy.