Contribution of (n, y) Reaction in the Out-of-Field Absorbed Dose for Patients under Radiotherapy Treatments with High MV Linear Accelerators

Abstract:

Although radiotherapy treatments at high energy offer important benefits for patients with several forms of cancer, there was a concern related to generation of neutrons through photonuclear reactions and their contribution to the delivered radiation dose. The debate about health hazards for patients reached a critical point. Mean free path in breast tissue as a function of energy for neutrons produced by photonuclear reactions with a 15 MV linear accelerator for the out-of-field region. For a mean free path bigger than 2.5 cm (1 MeV neutrons) the contribution of reactions related to neutrons to the absorbed dose can be neglected. when a recommendation for deterrence in the use of high energy beams was issued. More recent Monte Carlo simulations lead to much lower neutron dose equivalent and risk estimations with large uncertainties. In this work an alternative approach which is based on transport theory and neutron mean free paths for different tissues provides an upper bound of 1 MeV for the relevant energy range related to15 MV linear accelerators. In that energy range there are just two processes to be considered, namely, elastic scattering and (η, γ) reactions. The contribution of the (η, γ) reactions to the out of field absorbed dose is evaluated in detail for several tissues by taking into account gamma rays and beta emission decay chain for every nuclide. In the same way the enhancement effect on the absorbed dose which is produced by multiple scattering is evaluated through transport theory considerations. The resultant absorbed dose does not pose any significant health hazard.

Año de publicación:

2013

Keywords:

Fuente:

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