Author: Jean Dessureault, Malcolm R. McEwen, Bryan R. Muir, James Renaud 👨🔬
Affiliation: National Research Council 🌍
Purpose: To develop and commission a mailable calorimeter that enables clinical medical physicists to quickly and efficiently address innovative dosimetry challenges directly at the point of use.
Methods: A rugged twin-calorimeter system was designed using graphite and pure aluminum as absorbing materials. Housed within a compact polystyrene enclosure, the two calorimeters are nominally identical except for their material composition, and are placed at the same (but adjustable) measurement depth. This dual-material approach provides independent measurements of absorbed dose to water and cross-verifies system performance in remote settings. Commissioning experiments were conducted in clinical photon and electron beams to assess reproducibility and evaluate the response ratio of the two calorimeters. Subsequently, the system was shipped internationally for remote measurements in a range of electron FLASH irradiator beams. After an initial training session with on-site and remote support, a clinical medical physicist successfully operated the calorimeter system independently to collect data.
Results: For sets of ten repeated runs, delivering doses between 5 Gy and 12 Gy per run, the standard deviation of the calorimeter-measured dose was less than 0.3 %. The graphite-to-aluminum calorimeter response ratio was consistent at both “home” and “remote” sites, with variations at the 0.3 % level for comparable beam qualities. This suggests that shipping had no significant impact on system performance. Feedback from the host clinical site confirmed that the calorimeter system was easy to operate. The overall projected uncertainty of 0.5 % on the calorimeter dose-to-medium determination is not substantially larger than reported by national metrology institutes.
Conclusion: The twin-calorimeter system demonstrated reliable performance with a previously unexperienced user in a remote clinical environment. Its robust design and ease of use enable medical physicists to perform absolute dose measurements, addressing modern dosimetry challenges with the highest achievable accuracy.