Examination of Stability and Heat Transfer Effects of a Graphite Probe Calorimeter
N MacKay1*, F Keszti1, J Seuntjens2, A Sarfehnia3, J Renaud4, (1) McGill University, Montreal, QC, CA, (2) University Health Network, Toronto, ON, (3) Sunnybrook Health Science Center, Toronto, ON, CA, (4) National Research Council Canada, Ottawa, ON
Presentations
TH-B-BRA-4 (Thursday, 7/14/2022) 8:30 AM - 9:30 AM [Eastern Time (GMT-4)]
Ballroom A
Purpose: To experimentally characterize two prototype graphite calorimeters for accurate dosimetry through direct comparisons against a calibrated reference class ion chamber in high-energy photon beams. These calorimeters have been uniquely designed as hand-held devices for portability and ease of use in the clinical environment. For both Prototypes, the detectors’ stability over time and the correction factors required for clinical implementation were examined.
Methods: The Aerrow MK-V and MK-VII were irradiated in a water-equivalent phantom over a period of eight months in quasi-adiabatic mode to assess the stability of the response. In quasi-adiabatic mode, the calorimeter is used as a sensitive thermometer to measure the radiation-induced temperature rise. The Aerrow MK-V and Aerrow MK-VII were irradiated with a 10 MV FFF beam (400 MU; 2400 MU/min) 57 times and 47 times, respectively, over eight months. Three irradiations of the 10 MV FFF beam (400 MU, 685.7 MU and 1600 MU) were also used to investigate the time-dependant effects of heat transfer on different signal analysis methods.
Results: The response of the MK-V and MK-VII was stable with a standard deviation from the mean of 0.3% and 0.7%, respectively, throughout the study.The heat transfer study revealed that the conventional analysis method resulted in a (4.9 ± 0.2)% increase in response upon increasing the irradiation period from 10s to 40s. In contrast, an alternate analysis technique focused on determining the initial dose rate showed a near-complete elimination of the heat transfer dependence.
Conclusion: This work experimentally validates the dosimetric qualities of the Aerrow calorimetry system. The MK-V and MK-VII are stable to within 0.3% and 0.7%, respectively, over several months when operated quasi-adiabatically. A novel signal analysis method, minimally affected by heat transfer effects, has also been presented.
Keywords
Dose Response, Absolute Dosimetry, Thermal Dosimetry
Taxonomy
TH- Radiation Dose Measurement Devices: Development (new technology and techniques)
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