Purpose:
Use the methodology developed by the National Research Council Canada (NRC), for Fricke Dosimetry, to determine the G‐value used at Ir‐192 energies.
Methods:
In this study the Radiology Science Laboratory of Rio de Janeiro State University (LCR),based the G‐value determination on the NRC method, using polyethylene bags. Briefly, this method consists of interpolating the G‐values calculated for Co‐60 and 250 kV x‐rays for the average energy of Ir‐192 (380 keV). As the Co‐60 G‐value is well described at literature, and associated with low uncertainties, it wasn't measured in this present study. The G‐values for 150 kV (Effective energy of 68 keV), 250 kV (Effective energy of 132 keV)and 300 kV(Effective energy of 159 keV)were calculated using the air kerma given by a calibrated ion chamber, and making it equivalent to the absorbed to the Fricke solution, using a Monte Carlo calculated factor for this conversion. Instead of interpolations, as described by the NRC, we displayed the G‐values points in a graph, and used the line equation to determine the G‐ value for Ir‐192 (380 keV).
Results:
The measured G‐values were 1.436 ± 0.002 µmol/J for 150 kV, 1.472 ± 0.002 µmol/J for 250 kV, 1.497 ± 0.003 µmol/J for 300 kV. The used G‐value for Co‐60 (1.25 MeV) was 1,613 µmol/J. The R‐square of the fitted regression line among those G‐value points was 0.991. Using the line equation, the calculate G‐value for 380 KeV was 1.542 µmol/J.
Conclusion:
The Result found for Ir‐192 G‐value is 3,1% different (lower) from the NRC value. But it agrees with previous literature results, using different methodologies to calculate this parameter. We will continue this experiment measuring the G‐value for Co‐60 in order to compare with the NRC method and better understand the reasons for the found differences.
Purpose
For x‐ray beams in the low and medium energy range, reference dosimetry is established in terms of air kerma. Fricke dosimetry has shown great potential in the absolute measurements of the absorbed dose to water for high‐energy ranges. Therefore, the main purpose of this work was to compare the absorbed dose to water for medium‐energy x‐ray beams obtained through Fricke dosimetry with that obtained from the air kerma rate.
Methods
To determine the absorbed dose to water using Fricke dosimetry, the polyethylene bags methodology was chosen. Fricke solution was irradiated at four different beam qualities. The absorbed dose to water values obtained using Fricke dosimetry were compared to those obtained using the standard protocol, using the Z‐score.
Results
Values of the Z‐score were <2 for all measurements of absorbed dose to water, which means that the values obtained using Fricke dosimetry are equivalent to those obtained using the reference protocol. The combined standard uncertainty for the absorbed dose to water obtained by Fricke dosimetry was lower than that obtained with the ionization chamber.
Conclusions
Chemical dosimetry using a standard FeSO4 solution has been demonstrated to be a potential option as a standard for the quantity absorbed dose to water for medium kV x‐ray qualities.
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