Fricke dosimetry: the difference betweenG(Fe³⁺) for⁶⁰Co gamma-rays and high-energy x-rays

Abstract

A calibration of the Fricke dosimeter is a measurement of epsilon G(Fe3+). Although G(Fe3+) is expected to be approximately energy independent for all low-LET radiation, existing data are not adequate to rule out the possibility of changes of a few per cent with beam quality. When a high-precision Fricke dosimeter, which has been calibrated for one particular low-LET beam quality, is used to measure the absorbed dose for another low-LET beam quality, the accuracy of the absorbed dose measurement is limited by the uncertainty in the value of G(Fe3+). The ratio of G(Fe3+) for high-energy x-rays (20 and 30 MV) to G(Fe3+) for 60Co gamma-rays, G(Fe3+)MV(Co), was measured to be 1.007(+/-0.003) (confidence level of 68%) using two different types of water calorimeter, a stirred-water calorimeter (20 MV) and a sealed-water calorimeter (20, 30 MV). This value is consistent with our calculations based on the LET dependence of G(primary products) and, as well, with published measurements and theoretical treatments of G(Fe3+).

Dosimetric proprieties of FBX dosimeter for high energy photon and electron beams

“…The results showed that long term reproducibility is 0.2%. It was found to be similar with data reported for standard Fricke dosimeter in the literature [16]. The results in this study support the conclusion that the FBX is a good practical clinical dosimeter.…”

A standard Fricke dosimeter compared to an ionization chamber used for dosimetric characterization of 60Co photon beam

“…The absorbance readings were corrected for the influence of both the readout temperature, T r , and the irradiation temperature, T i . The linear interval investigated is consistent with the results reported elsewhere [14] and is adequate for radiotherapy purposes. From the result above, by equating D w,F in equation 2 to the absorbed dose to water measured by the reference ionization chamber, D w , we calculate the radiation yield of Fe ) to be 1.598 (±0.012) µmol j −1 .…”

Fricke gel dosimeter with improved sensitivity for low‐dose‐level measurements

“…First of all it should be emphasized that the overall performance of the developed dosimetric system exhibits typical characteristics of gel dosimeters, like linear response within dose range of interest, 1 , 6 reproducibility, 3 , 6 , 11 tissue‐equivalence, 2 , 3 , 11 and quite negligible photon beam energy dependence 1 , 2 , 5 , 8 , 9 …”

“…It is noteworthy that dosimetry systems based on FXG have significant advantages: high lighted tissue equivalence, beam quality independence ( a priori , at least to conventional techniques (i.e., not hadronic)), regardless of both quasi‐linear energy transfer 3 , 4 , 5 , 6 , 7 and dose rate 3 , 5 , 8 , 9 . Although diffusion of ferric ions represents a nonnegligible drawback, 1 , 2 , 3 , 10 suitable preparation/manipulation protocols along with prompt analysis provided to FXG the capability to obtain three‐dimensional dosimetry mappings.…”