The measurement of neutron contamination in high energy x-ray radiotherapy using He-3 gas dosimeter

Document Type : Original Paper


1 Physics Department, Faculty of Sciences, University of Neyshabur, Neyshabur, Iran

2 Medical Physics Department, Faculty of Medicine, Imam Reza Center of Medical Education and Treatment, Mashhad, Iran

3 Medical Physics Department, Faculty of Medicine, Gonabad University of Medical Sciences, Gonabad,Iran

4 Medical Physics and Radiological Sciences Department, Sabzevar University of Medical Sciences

5 department of medical physics and radiological sciences, Sabzevar university of medical sciences, Sabzevar, Iran



Introduction: Neutron contamination is likely caused by the collision of high-energy photon interactions (γ, ṉ) with heavy metals used in the construction of the accelerator. The main object is to assess the neutron contamination with a gas dosimeter containing He-3.

Methods: In this study, neutron contamination was estimated at different points in and out of the treatment room. We used two types of dosimeters: a He-3 gas dosimeter (CRAMAL 31) as a neutron dosimeter and Farmer ionization chambers, and PC-electrometer (Sun Nuclear, USA) which is sensitive to photons measured photo-neutron doses. Both the neutron and Farmer dosimeters were applied in the presence and absence of acrylic plates at the same point. In this study, MCNPX2.6.0 Monte Carlo (MC) code was utilized to prepare the correct proportion of neutron dose.

Results: At different points in and out of the treatment room, neutron contamination was approximately in the range of background dose (D = 0.001 µSv). The neutron dosimeter displayed 48.792 µSv, 25.456 µSv and 28.756 µSv for 6, 10 and 15 MeV photon energy, respectively. A He-3 gas dosimeter showed that the neutron dose net was negligible under the treatment field.

Conclusion: A He-3 gas dosimeter detected more than the usual neutron dose in 6 MeV photon energy than we expected. Due to the high photon flux under the radiation fields, A He-3 neutron dosimeter reported photo-neutron dose. Nevertheless, the photo-neutron dose was in the range of micro Sievert (µSv). A He-3 gas dosimeter was not suitable for neutron dosimetry in places with high photon fluence because of the low energy peak in the detection of neutrons.


Main Subjects

Articles in Press, Accepted Manuscript
Available Online from 14 January 2024
  • Receive Date: 10 October 2023
  • Revise Date: 12 December 2023
  • Accept Date: 14 January 2024