A water calorimeter for neutron dosimetry

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Neutron Beam Therapy

Background:

• Accurate absorbed dose determination is crucial for radiation therapy.
• Discrepancies exist between different dosimetry methods, particularly for neutron beams.
• The heat defect in water can influence calorimetric measurements.

Purpose of the Study:

• To directly measure absorbed dose to water using a water calorimeter in a d(15) + Be neutron beam.
• To compare calorimeter-based dosimetry with ionisation chamber measurements.
• To investigate the implications of the heat defect in water for neutron dosimetry.

Main Methods:

• Utilized a water calorimeter for direct absorbed dose measurement.
• Employed an Exradin ionisation chamber (A-150 plastic) for comparison.
• Calculated ionisation chamber doses following the European (ECNEU) protocol.

Main Results:

• Calorimetric absorbed dose to tissue was 4.3% lower than ionisation chamber measurements.
• Neutron beam dose measurements with the calorimeter were 9% lower compared to photon beams (4 and 9 MV).
• Results suggest a significant contribution of the heat defect in water.

Conclusions:

• Water calorimetry provides a direct measure of absorbed dose, revealing discrepancies with ionisation chambers in neutron beams.
• The observed differences underscore the importance of considering the heat defect in water for accurate dosimetry.
• Further research is needed to refine neutron dosimetry protocols and understand calorimetric responses.