Exhibit Hall | Forum 4
Purpose: Water calorimeters (WCs) determine absolute dose to water directly by measuring the radiation-induced temperature rise. Complexities with design/operation have made WCs use limited to standard laboratories. We have built a novel portable MR-compatible WC that can be used in clinics for measurements under some of the most complex technologies (MR-linac, GammaKnife®). Traditionally, a Pyrex-glass vessel is at the heart of a calorimeter encompassing thermistors, temperature-sensitive detectors. To make our WC versatile, we investigated the suitability of a 3D-printed vessel for WC by studying the heat defect correction which results from heat loss/gain due to impurities in water.
Methods: A 3D-printed Accura ClearVUE® vessel with a similar design as our traditional Pyrex vessel was built, filled with high-purity water, saturated with high-purity H(2) gas, pre-irradiated with 100Gy, and was sealed inside our in-house built WC and cooled down to 4°C. Heat defect as a function of time, accumulated dose, dose rate, and energy for this system was studied. To first order, heat defect was experimentally determined by comparing absorbed dose measured by calorimeter against reference dose measured under identical conditions using a calibrated, standard-laboratory traceable Exradin A1SL chamber.
Results: Calorimeter measurements periodically taken over a one month period (600 hours) showed a stable output (1σ = 0.24%). In addition, the response was unaffected by accumulated dose over 3000Gy. Heat defect for 6MV flattening filter-free, 6MV, and 18MV beam was determined to be 1.000±0.009, 0.995±0.009, 0.991±0.009, respectively.
Conclusion: Heat defect was determined for a 3D-printed vessel and was found to be stable over long periods and high accumulated doses, suggesting that novel versatile 3D-printed vessel designs may be used for WC if taking into account a stable, yet non-zero heat defect. Water calorimetry in volumetric delivery (VMAT) and GammaKnife® using this approach is currently underway.
Funding Support, Disclosures, and Conflict of Interest: This work has been supported in part by a Discovery grant of the Natural Sciences and Engineering Research Council (NSERC; Grant No. RGPIN-435608)