Photoneutron Distributions around 18 MV Xray Radiotherapy Accelerators using Nuclear Track Detectors

1
Photoneutron Distributions around 18 MV X-ray
Radiotherapy Accelerators using Nuclear Track
Detectors

• Fazal-ur-Rehman,
• H. Al-Ghamdi,
• M. I. Al-Jarallah (Presenting Author)
• N. Maalej

King Fahd University of Petroleum and Minerals
2
Outline

• Introduction
• Methods
• Results
• Conclusion

3
Introduction

• Neutrons contaminate the high energy Linear
  Accelerator (LINAC) photon beam in radiation
  therapy and contribution dose to the patient
• We studied the distribution of thermal and fast
  neutrons in the LINAC room during irradiation
  with an 18 MeV photon beam

4
Methods

• Neutrons are generated by high energy photon
  interaction with the high Z materials of the
  LINAC head
• Fast Neutron Measurement
• Bare NTDs are used
• Tracks are generated by protons from the (n,p)
  recoil in the detector material (C12H18O7 )
• Thermal Neutron Measurement
• NTDs are covered with Li2B4O7
• Tracks are generated by ?-particles from
  10B(n,?)7Li and 6Li(n,?)3H nuclear reactions

5
Methods
Fig.1 Experimental arrangement showing the
location of CR-39 NTDs around a radiotherapy
linear accelerator.
6
Methods
x
Fig. 2 Experimental arrangement showing the
location of CR-39 NTDs around a radiotherapy
linear accelerator.
7
Methods

• NTDs advantages over active detectors
• There is no pulse pileup problem
• No photon interference with neutron measurement
• No electronics are required
• Less prone to noise and interference

8
Results
Fig. 4 Fast neutron relative intensity as a
function of transversal distance from isocenter
of linear accelerators located in a small and
large treatment rooms.
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Results
Fig. 5 Fast neutron relative intensity as a
function of longitudinal distance from the
isocenter of linear accelerators located in a
small and large treatment rooms.
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Results
Fig. 6 Fast neutron relative intensity as a
function of longitudinal distance from the
isocenter of linear accelerators located in a
small and large treatment rooms.
11
Results
Fig. 7 Thermal neutron relative intensity as a
function of longitudinal distance from isocenter
of linear accelerators located in a small and
large treatment rooms.
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Conclusion

• The fast neutron distribution along the
  transverse and longitudinal directions is
  symmetrical about the beam axis.
• The fast neutron relative intensities fall in an
  exponential-like fashion with distance from the
  isocenter of the accelerators.
• The thermal neutron distribution is uniform at
  all the locations along transverse and
  longitudinal directions.
• The larger size LINAC room had lower fast and
  thermal neutron relative intensities at all
  locations.

13
Acknowledgment

• Physics Department of King Fahd University of
  Petroleum and Minerals (KFUPM).
• The Department of Radiotherapy, King Fahd
  Specialist Hospital.
• Dhahran Health Center, Dhahran, for utilizing
  their accelerator facilities in this study.