Displacement correction factor for fast-neutron dosimetry in a tissue-equivalent phantom

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Neutron Therapy

Background:

• Accurate fast-neutron dosimetry is crucial for effective neutron radiotherapy.
• Tissue-equivalent ion chambers are commonly used for these measurements.
• The presence of the ion chamber can displace phantom material, affecting dose measurements.

Purpose of the Study:

• To investigate and determine the displacement correction factor for air-filled EG and G tissue-equivalent ion chambers.
• To evaluate the dependence of this factor on phantom depth and neutron beam size.

Main Methods:

• Measurements were performed using the MANTA neutron radiotherapy beam (35-MeV deuterons on Be target).
• Two EG and G ion chambers (IC-17: 1.0 cm3 and IC-18: 0.1 cm3) were used.
• The displacement correction factor was inferred from dosimetric measurements in a tissue-equivalent phantom.

Main Results:

• The displacement correction factor was found to be 0.970 for the IC-17 chamber.
• The displacement correction factor was found to be 0.989 for the IC-18 chamber.
• No significant dependence of the displacement correction factor on phantom depth or neutron beam size was observed.

Conclusions:

• The determined displacement correction factors are essential for accurate analysis of fast-neutron dosimetry data.
• These factors improve the reliability of dose calculations in neutron radiotherapy.
• The findings support the use of these ion chambers with the derived correction factors in clinical settings.