Journal of Medical Physics
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ORIGINAL ARTICLE
Year : 2015  |  Volume : 40  |  Issue : 2  |  Page : 90-94

Photo neutron dose equivalent rate in 15 MV X-ray beam from a Siemens Primus Linac


1 Department of Radiotherapy, Faculty of Medicine, Mazandaran University of Medical Sciences, Sari, Iran
2 Department of Biochemistry and Biophysics, Faculty of Medicine, Mazandaran University of Medical Sciences, Sari, Iran
3 Nuclear Science and Technology Research Institute, Tehran 14395-836, Iran
4 Department of Nuclear Engineering, Islamic Azad University, Sciences and Researches Branch, Tehran, Iran

Correspondence Address:
Dr. T Allahverdi Pourfallah
Department of Biochemistry and Biophysics, Faculty of Medicine, Mazandaran University of Medical Sciences, Sari
Iran
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0971-6203.158681

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Fast and thermal neutron fluence rates from a 15 MV X-ray beams of a Siemens Primus Linac were measured using bare and moderated BF 3 proportional counter inside the treatment room at different locations. Fluence rate values were converted to dose equivalent rate (DER) utilizing conversion factors of American Association of Physicist in Medicine's (AAPM) report number 19. For thermal neutrons, maximum and minimum DERs were 3.46 × 10 -6 (3 m from isocenter in +Y direction, 0 × 0 field size) and 8.36 × 10 -8 Sv/min (in maze, 40 × 40 field size), respectively. For fast neutrons, maximum DERs using 9" and 3" moderators were 1.6 × 10 -5 and 1.74 × 10 -5 Sv/min (2 m from isocenter in +Y direction, 0 × 0 field size), respectively. By changing the field size, the variation in thermal neutron DER was more than the fast neutron DER and the changes in fast neutron DER were not significant in the bunker except inside the radiation field. This study showed that at all points and distances, by decreasing field size of the beam, thermal and fast neutron DER increases and the number of thermal neutrons is more than fast neutrons.


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