Nuclear Engineering and Technology

Korean Nuclear Society (한국원자력학회)
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Measurement of Photo-Neutron Dose from an 18-MV Medical Linac Using a Foil Activation Method in View of Radiation Protection of Patients

  • Yucel, Haluk (Ankara University, Institute of Nuclear Sciences) ;
  • Cobanbas, Ibrahim (Suleyman Demirel University, School of Medicine, Department of Radiation Oncology) ;
  • Kolbasi, Asuman (Ankara University, Institute of Nuclear Sciences) ;
  • Yuksel, Alptug Ozer (Ankara University, Institute of Nuclear Sciences) ;
  • Kaya, Vildan (Suleyman Demirel University, School of Medicine, Department of Radiation Oncology)
  • Received : 2014.10.27
  • Accepted : 2015.11.07
  • Published : 2016.04.25
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Abstract

High-energy linear accelerators are increasingly used in the medical field. However, the unwanted photo-neutrons can also be contributed to the dose delivered to the patients during their treatments. In this study, neutron fluxes were measured in a solid water phantom placed at the isocenter 1-m distance from the head of an18-MV linac using the foil activation method. The produced activities were measured with a calibrated well-type Ge detector. From the measured fluxes, the total neutron fluence was found to be $(1.17{\pm}0.06){\times}10^7n/cm^2$ per Gy at the phantom surface in a $20{\times}20cm^2$ X-ray field size. The maximum photo-neutron dose was measured to be $0.67{\pm}0.04$ mSv/Gy at $d_{max}=5cm$ depth in the phantom at isocenter. The present results are compared with those obtained for different field sizes of $10{\times}10cm^2$, $15{\times}15cm^2$, and $20{\times}20cm^2$ from 10-, 15-, and 18-MV linacs. Additionally, ambient neutron dose equivalents were determined at different locations in the room and they were found to be negligibly low. The results indicate that the photo-neutron dose at the patient position is not a negligible fraction of the therapeutic photon dose. Thus, there is a need for reduction of the contaminated neutron dose by taking some additional measures, for instance, neutron absorbing-protective materials might be used as aprons during the treatment.

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References

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