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Neutron and photon spectra in LINACs
H R Vega-Carrillo1, S A Martínez-Ovalle, A M Lallena
1Unidad Academica de Estudios Nucleares, Universidad Autónoma de Zacatecas, C Cipres 10, Fracc La Peñuela, 98060 Zacatecas, Zac, Mexico. fermineutron@yahoo.com
Summary
This study used Monte Carlo simulations to analyze photon and neutron spectra from medical linear accelerators (linacs). Results show consistent spectral features across different voltages, aiding radiation therapy safety.
Area of Science:
- Medical Physics
- Radiation Oncology
- Computational Physics
Background:
- Linear accelerators (linacs) are crucial in radiation therapy.
- Accurate characterization of photon and neutron spectra is essential for treatment planning and safety.
- Understanding radiation fields produced by linacs operating at different energies (15 and 18 MV) is important.
Purpose of the Study:
- To estimate photon and neutron spectra in specific locations within two medical linacs.
- To compare simulated neutron spectra with existing models.
- To investigate the influence of linac voltage on radiation spectra.
Main Methods:
- Utilized the MCNPX Monte Carlo code for detailed simulations.
- Modeled linac heads precisely to capture radiation transport.
- Calculated spectra below the flattening filter and at the isocenter.
Main Results:
- Neutron spectra exhibit two distinct components: evaporation and knock-on.
- The Tosi et al. function reasonably describes neutron spectra above 1 MeV but underestimates lower energies.
- Photon (Bremsstrahlung) and neutron spectra displayed consistent characteristics irrespective of linac operating voltage (15 vs. 18 MV).
Conclusions:
- Monte Carlo simulations provide valuable insights into linac radiation fields.
- The Tosi et al. model has limitations in accurately representing low-energy neutron spectra.
- Linac voltage has a negligible impact on the fundamental features of photon and neutron spectra.
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