Towards Absolute Dose Measurement in MRI-LINAC and GAMMA KNIFE®: Design and Construction of an MR-Compatible Water Calorimeter

The purpose of this work was to design and build a portable 4⁰C stagnant Water Calorimeter (WC) for dual use in MRI-linac and Gamma Knife® in addition to conventional radiotherapy linacs. WC determines radiation energy absorbed in a sensitive volume absolutely and directly through measuring radiation-induced temperature rise (related to the medium’s specific heat capacity). To assist with the design process, several parameters involved in calorimeter tank design including tank dimensions, a variety of insulation material and thicknesses, unique cooling design structures to sustain WC at 4⁰C, as well as the calorimeter vessel design were simulated, and the results on heat gain/loss at the point of measurement was evaluated. Based on the optimizations, a calorimeter tank was built, and one single set of initial measurements in a conventional clinical linear accelerator was performed.