دانلود رایگان مقاله مطالعه مونت کارلو معادل دوز نوترون محیط به بیمار در اتاق درمان

Abstract

This paper presents an analytical method for the calculation of the neutron ambient dose equivalent H* (10) regarding patients, whereby the different concrete types that are used in the surrounding walls of the treatment room are considered. This work has been performed according to a detailed simulation of the Varian 2300C/D linear accelerator head that is operated at 18 MV, and silver activation counter as a neutron detector, for which the Monte Carlo MCNPX 2.6 code is used, with and without the treatment room walls. The results show that, when compared to the neutrons that leak from the LINAC, both the scattered and thermal neutrons are the major factors that comprise the out-of field neutron dose. The scattering factors for the limonite-steel, magnetite-steel, and ordinary concretes have been calculated as 0.91±0.09, 1.08±0.10, and 0.371±0.01, respectively, while the corresponding thermal factors are 34.22±3.84, 23.44±1.62, and 52.28±1.99, respectively (both the scattering and thermal factors are for the isocenter region); moreover, the treatment room is composed of magnetite-steel and limonite-steel concretes, so the neutron doses to the patient are 1.79 times and 1.62 times greater than that from an ordinary concrete composition. The results also confirm that the scattering and thermal factors do not depend on the details of the chosen linear accelerator head model. It is anticipated that the results of the present work will be of great interest to the manufacturers of medical linear accelerators.

4. Conclusion

This work presents the simulation results of the neutron dose from a medical LINAC to the patient with and without treatment room walls that are made of three different concrete types; for this purpose, the Monte Carlo N-particles MCNPX 2.6 code has been used. The results provide detailed information on the neutron contributions from the walls of the different concretes, and they also confirm that the neutron dose is increased through the scattering that is off the walls of the treatment room. To reduce the thermal neutron dose it is necessary to use a thin layer of the thermal neutron absorber material around the patient body, with the exception of the desired photon pathway. Also, to reduce the neutron dose to the patient, a treatment room with low scattering and thermal factors is recommended.