title: Study on the measurement of photo-neutron for15 MV photon beam from medical linear accelerator under different irradiation geometries using passive detectors.
abstract: OBJECTIVE
  The photo-neutron dose equivalents of 15 MV Elekta precise accelerators were measured for different depths in phantom, for various field sizes, at different distances from the isocenter in the patient plane and for various wedged fields.
  
  
  METHODS
  Fast and thermal neutrons are measured using passive detectors such as Columbia Resin-39 and pair of thermoluminescent dosimetry (TLD) 600 and TLD 700 detector from Elekta medical linear accelerator.
  
  
  RESULTS
  It is found that fast photo-neutron dose rate decreases as the depth increases, with a maximum of 0.57 ± 0.08 mSv/Gy photon dose at surface and minimum of 0.09 ± 0.02 mSv/Gy photon dose at 15 cm depth of water equivalent phantom with 10 cm backscatter. Photo neutrons decreases from 1.28 ± 0.03 mSv/Gy to 0.063 ± 0.032 when measured at isocenter and at 100 cm far from the field edge along the longitudinal direction in the patient plane. Fast and thermal neutron doses increases from 0.65 ± 0.05 mSv/Gy to 1.08 ± 0.07 mSv/Gy as the field size increases; from 5 cm × 5 cm to 30 cm × 30 cm for fast neutrons. With increase in wedge field angle from 0° to 60°, it is observed that the fast neutron dose increases from 0.42 ± 0.03 mSv/Gy to 0.95 ± 0.05 mSv/Gy.s
  
  
  CONCLUSIONS
  Measurements indicate the photo-neutrons at few field sizes are slightly higher than the International Electrotechnical Commission standard specifications. Photo-neutrons from Omni wedged fields are studied in details. These studies of the photo-neutron energy response will enlighten the neutron dose to radiation therapy patients and are expected to further improve radiation protection guidelines.
authors.affiliation: Department of Physics, Noorul Islam Centre for Higher Education, Noorul Islam University, Kanyakumari, Tamil Nadu; Department of Medical Physics, Dr. Balabhai Nanavati Hospital, Mumbai, Maharashtra, India.
authors.forename: Siji Cyriac
authors.initials: SC
authors.lastname: Thekkedath
authors.affiliation: Department of Physics, Noorul Islam Centre for Higher Education, Noorul Islam University, Kanyakumari, Tamil Nadu, India.
authors.forename: R Ganapathi
authors.initials: RG
authors.lastname: Raman
authors.affiliation: Department of Physics, University of Calicut, Malappuram, Kerala, India.
authors.forename: M M
authors.initials: MM
authors.lastname: Musthafa
authors.affiliation: Bhabha Atomic Research Center, Radiological Physics and Advisory Division, Mumbai, Maharashtra, India.
authors.forename: A K
authors.initials: AK
authors.lastname: Bakshi
authors.affiliation: Bhabha Atomic Research Center, Radiological Physics and Advisory Division, Mumbai, Maharashtra, India.
authors.forename: Rupali
authors.initials: R
authors.lastname: Pal
authors.affiliation: Bhabha Atomic Research Center, Radiological Physics and Advisory Division, Mumbai, Maharashtra, India.
authors.forename: Sandipan
authors.initials: S
authors.lastname: Dawn
authors.affiliation: Department of Medical Physics, Dr. Balabhai Nanavati Hospital, Mumbai, Maharashtra, India.
authors.forename: Abdul Haneefa
authors.initials: AH
authors.lastname: Kummali
authors.affiliation: Department of Medical Physics, Dr. Balabhai Nanavati Hospital, Mumbai, Maharashtra, India.
authors.forename: Nagraj G
authors.initials: NG
authors.lastname: Huilgol
authors.affiliation: Bhabha Atomic Research Center, Radiological Physics and Advisory Division, Mumbai, Maharashtra, India.
authors.forename: T Palani
authors.initials: TP
authors.lastname: Selvam
authors.affiliation: Bhabha Atomic Research Center, Radiological Physics and Advisory Division, Mumbai, Maharashtra, India.
authors.forename: D
authors.initials: D
authors.lastname: Datta
mesh_terms: D005720:Gamma Rays; D006801:Humans; D009502:Neutrons; D010315:Particle Accelerators / Q000295:instrumentation; D019047:Phantoms, Imaging; D017785:Photons; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation / Q000379:methods; D015203:Reproducibility of Results