| Abstrakt: |
The process of setting up the treatment of patients involves several steps including the use of treatment planning system for dose distribution calculation. The main input data for dose calculation is the reference kerma rate; generally measured using well type chamber. For kerma rate calculations purposes, a kerma rate constant (Γ, δ,AKR) is used (that is the factor relates activity to kerma rate in air). The published data of Γ, δ,AKR are in strong disagreement because of the disagreement of the data used in the calculations. The values of the reference spectra of radionuclides and the mass energy transfer coefficients for air values need to be improved and updated regularly in order to use the most precise data to improve the accuracy of kerma rate calculation, which are fundamental for the absorbed dose calculation in brachytherapy. The objective of the present work is to use the reference spectra of radionuclides and the latest data for mass energy transfer coefficients for air to compute the kerma rate constant, for the most important photon emission sealed sources used in brachytherapy (137Cs, 192Ir and 60Co), to improve the accuracy of the air kerma rate calculation as well as the absorbed dose calculation to the soft tissue. The sources chosen for this study were 137Cs grain, 192Ir wire used for low dose rate and 60Co grain used for high dose rate brachytherapy. The spectra used were the reference spectra extracted from the Lund/LBNL nuclear data search database. The mass energy transfer coefficients used were extracted from the NIST X-ray attenuation databases. The result of this study shows a good agreement between computed Γ, δ AKR values and published data. Furthermore, good agreement were observed between calculated kerma rates using the reference energy spectra and the measured corresponding quantities using well type chamber with differences of 2.5%, 0.4% and 4.4% for 137Cs, 60Co, and 192Ir respectively. Therefore, for better estimation of the air kerma rate, the reference energy spectrum of the radionuclidet should be taken into account instead of the weighted average energies as well the updated data for mass energy transfer coefficients for air and energy spectra. [ABSTRACT FROM AUTHOR] |
