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Description
Introduction
The ideal detector for MR guided radiotherapy (MRgRT) applications is not influenced by the presence of a magnetic field during the irradiation. The Fricke-type detector is a chemical dosimetry method in which ferrous iron (Fe
Materials and Methods
The Fricke detector consists of a perfluoroakoxy alkane (PFA) sample cup filled to the top with an acidic ferrous iron solution. The detector readout was performed with a UV spectrophotometer (Varian Cary 6000i) by measuring the absorbance change of the solution upon irradiation and calculating the change of the Fe
Results
The linearity of the Fricke response curves between 6 Gy and 100 Gy is not influenced by the applied magnetic fields (0 T – 1.42 T) during the irradiation with a 6 MV photon beam. The magnetic field correction factors k_B for the Fricke detector for magnetic field strengths of 0.35 T and 1.42 T are 0.995±0.005 and 0.998±0.005, respectively.
Conclusion
The response of the Fricke detector is not significantly influenced by the presence of a magnetic field during the irradiation and the correction for the applied magnetic field is <0.5%. This correction is rather small in comparison to ionization chamber type detectors, which have corrections up to several percent dependent on the mutual orientation of the detector and the magnetic field.