He jishu (Jul 2024)
Absolute measurement of absorbed dose to water for γ-ray of 60Co by water calorimetry
Abstract
BackgroundMost of domestic radiation therapy doses can only be traced back to air kerma of 60Co γ-ray at present in China. The uncertainty of directly tracing radiation therapy dose to absorbed dose to water is much smaller compared to tracing radiation therapy dose to air kerma, which must be converted to absorbed dose to water.PurposeThis study aims to solve the problem of traceability and transfer of 60Co γ-ray absorbed dose to water, as well as the problem that the dose measurement of radiotherapy cannot be directly traced through the absorbed dose to water, NIMTT (National Institute of Measurement and Testing Technology) has established an absolute measurement device of 60Co γ-ray absorbed dose to water.MethodsAn absolute measurement device of 60Co γ-ray absorbed dose to water was established by National Institute of Measurement and Testing Technology (NIMTT) using water calorimeterfor direct measurement of absorbed dose to water. The correction factors for water absorbed dose measurement were obtained by experimental and simulation methods. A comparison of laboratory reproducing results was made between NIMTT and NRC (National Research Council, Canada) using the method of transmitting standard to further verify the accuracy and consistency of the measurement of 60Co γ-ray absorbed dose to water. Two PTW ionization chambers were used as the transfer standard.ResultsThe reproduced results of two laboratories for absolute measurement of 60Co γ-ray absorbed dose to water are consistent within the relative standard uncertainty of 0.71%, and the normalized error value of En is -0.45.ConclusionsThe comparison results have verified that NIMTT laboratory has the ability of traceability and transmission of absorbed dose to water. The results of this study provide a reference for the absolute measurement of absorbed dose to water for 60Co γ-ray.
Keywords
