Program Information
Design of a Water Calorimeter for Dual Use in An Integrated MRI-Linac and Gamma-Knife
N Entezari1*, J Renaud2 , D Ly3 , A Sarfehnia4 , (1) Ryerson University, Toronto, Ontario, (2) McGill University, Montreal,, Quebec, (3) Waterloo University, Waterloo, Ontario, (4) Sunnybrook Hospital, Toronto, ON
Presentations
SU-E-E-15 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To design a water calorimeter for dual use in an integrated MRI-linac and Gamma-Knife. In calorimetry, dose to water is measured based on the assumption that energy absorbed in a sensitive volume is completely converted to temperature rise ₍ΔΤ₎ according to the specific heat capacity of the medium c: D=c*ΔT*k, where k is heat transfer correction factor and compensates for heat gain or loss at point of measurement due to conductive effects.
Methods: A commercial finite element method software package was used to model four different water calorimeter designs. The long term (48 h) thermal stability of each design was accurately modeled, and the optimization of the final design was based on evaluation of the standard deviation of k for ten consecutive irradiation runs (lower standard deviation translates to greater thermal stability). Several insulator materials of varying thicknesses were investigated, and a sensitivity study of thermal stability to variations in ambient temperature fluctuations was undertaken. Specifically, we evaluated the effect of possible variations in coolant temperature circulating around the calorimeter tank in several scenarios (constant, slowly increasing, or fluctuating).
Results: Due to MRI-compatibility requirements, the calorimeter is to be built entirely out of plastic. Among all insulation materials tested, solid state aerogel-based insulation resulted in least heat loss and thermal stability. The final design is cylindrical on top (to be used upright in MRI-linac) and semi-spherical at bottom (for use in GammaKnife). The range of k was found to be 1.002 ± 0.013 (k = 1), comparable with a k of 1.002 ± 0.014 for typical water calorimeters used in high energy beams. A long term stability of 0.36 μK/hr was evaluated.
Conclusion: Optimization of a water calorimeter design for dual use in MRI-linac and Gamma-Knife has been completed and the device is currently in production.
Funding Support, Disclosures, and Conflict of Interest: Supported by NSERC RGPIN 435608
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