Development of a new in-water-phantom graphite calorimeter for the measurement of absorbed dose to water in medium energy x-ray beams

This paper summarizes the progress on the construction of a graphite calorimeter for the measurement of absorbed dose to water Dw in medium-energy filtered x-ray qualities, as part of the EMRPfunded project “Metrology for radiotherapy using complex radiation fields” (MetrExtRT, http://radiotherapyemrp.eu/). The design and the construction of a new primary standard for absorbed dose to water (Dw) is shown, together with a presentation of the preliminary estimates of conversion factors, calculated by Monte Carlo using the EGSnrc code, and heat-transport calculations resulting from COMSOL simulations. The vacuum-gap-insulated calorimeter core has a thickness of 2 mm and a diameter of 20 mm. The graphite calorimeter is embedded in a PMMA waterproof sleeve and can be positioned at the desired measurement depth in a water phantom. Once completed, the new calorimeter will participate in an international comparison with other existing standards of absorbed dose to water for medium energy x-rays.