Development of Methods and Tools for Determining the Absorbed Dose Rate in Water from Brachytherapy Sources Taking into Account Actual Radiation Spectra

The article presents a developed methodology for measuring the absorbed dose rate to water from brachytherapy photon radiation sources. The proposed approach is based on the transition from absorbed dose measurements using a graphite calorimeter to the dose to water using special phantoms and ionization chambers. A key feature of the method is the application of refined conversion factors that consider the actual energy spectrum of the radiation, along with the calculation of correction factors accounting for the differences in measurement conditions between graphite and water using the Monte Carlo method. The developed solution makes it possible to achieve expanded uncertainty values of 1.2% (for sources with photon energies above 100 keV) and 3.2% (for sources with photon energies below 100 keV). When disseminating the unit, the expanded uncertainties are no more than 3% and 5%, respectively. The results of the work have practical significance for improving the metrological assurance of radiation therapy.