Encrypted login | home

Program Information

Development of An MRI-Compatible Water Calorimeter for Absolute Dosimetry in MRLinac and Gamma Knife

A Sarfehnia

A Sarfehnia1,2,3,4*, N Entezari3 , G Peterson1 , J Renaud4 , H Nusrat3 , (1) Sunnybrook Health Sciences Centre, Toronto, ON, (2) University of Toronto, Toronto, ON, (3) Ryerson University, Toronto, ON, (4) McGill University, Montreal, QC,


TU-FG-205-6 (Tuesday, August 1, 2017) 1:45 PM - 3:45 PM Room: 205

Purpose: Water calorimetry is a means of determining absolute absorbed radiation dose through a direct measurement of radiation-induced temperature rise. In this work, through a rigorous set of optimizations, we have designed and constructed a portable 4°C stagnant water calorimeter (WC) that is completely built from plastic and ceramic materials with no metallic/ferromagnetic components. The WC dimensions allow use in conventional linacs, as well as in MRI-linac and GammaKnife. Given our unique design and material choices, our WC is fully MRI-compatible and can be imaged with MRI or CBCT/MV.

Methods: A commercial finite element software was used to evaluate several WC designs with different unique cooling mechanism arrangements (to sustain 4°C), as well as different insulation materials and thicknesses. The evaluation was based on the magnitude of heat transfer away/into point of measurement due to non-radiation based environmental factors. The most optimal design was constructed in-house with preliminary tests underway.

Results: With our optimizations, we converged on a cylindrical water tank design with one hemispherical end. The tank wall consists of coolant channels being encompassed on either side by cryogel insulation. In this design, water temperature inside WC was least sensitive to environmental temperature variations (<1E-5 K/s).Initial T1 and T2 images of the WC (plus vessel) in a Philips 1.5T MRsim were obtained. The measuring thermistor tips were clearly visible with no artifacts showing the feasibility of positioning the tank using imaging. Preliminary measurements in a 6MV Elekta linac were promising. Typical heat drifts and ohm runs were observed. In response to our initial measurements, Small modifications to WC are underway, with future measurements planned.

Conclusion: An MR-compatible WC has been optimized, designed and built. WC can be fully imaged for accurate positioning, and initial measurements have been promising.

Funding Support, Disclosures, and Conflict of Interest: Funding provided by Natural Sciences and Engineering Research Council (NSERC) RGPIN 435608

Contact Email: