MONTE CARLO STUDY OF NEUTRON SPECTRA UNFOLDING FOR A PROTON BEAM USING MLEM.

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Nuclear Engineering

Background:

• Proton therapy generates secondary neutrons, contributing to stray radiation dose for patients and staff.
• Accurate assessment of neutron doses requires determining their energy spectrum.

Purpose of the Study:

• To simulate secondary neutron generation in a proton therapy accelerator head.
• To unfold the neutron energy spectrum using Monte Carlo (MC) simulations and a Maximum Likelihood Expectation Maximization (MLEM) algorithm.
• To evaluate the response of a newly designed Extended Bonner Sphere Spectrometer (EBSS) for high-energy neutron detection.

Main Methods:

• MC simulations were used to model neutron generation and detector response.
• An MLEM algorithm was employed for spectral deconvolution.
• The EBSS mesh model was simulated and its response evaluated.
• Simulations were conducted with the EBSS placed at specific distances from the accelerator head.

Main Results:

• The study successfully reproduced secondary neutron generation using MC simulations.
• The MLEM algorithm, coupled with the EBSS response, effectively deconvoluted the neutron fluence energy spectrum.
• Neutron spectra were unfolded in the absence of treatment room elements.

Conclusions:

• MC simulations and MLEM algorithms are viable tools for assessing neutron spectra in proton therapy.
• This methodology aids in the accurate evaluation of neutron doses in radiation oncology.
• The developed EBSS mesh model shows promise for high-energy neutron detection.