Potassium dithionate EPR dosimetry for determination of absorbed dose and LET distributions in different radiation qualities

With an increasing interest in using protons and light ions for radiation therapy there is a need for possibilities to simultaneously determine both absorbed dose ( D) and linear energy transfer, LET, ( L Δ). Potassium dithionate (K 2S 2O 6) tablets were irradiated in a conventional 6 MV linear accelerator photon beam and a N 7+ beam ( E = 33.5 MeV/u) respectively. The EPR spectrum of irradiated potassium dithionate is a narrow doublet consisting of two signals, R 1 and R 2 , with different microwave power saturation properties. On the basis of identification in related substances by EPR and ENDOR, these two signals are assigned to two non-equivalent SO 3 − – radicals. Our experiments showed that the ratios of these two lines ( R 1 / R 2 ) were clearly connected to beam LET. Irrespective of the mechanistic details this investigation suggests a new method for measurement of absorbed dose and beam LET by using potassium dithionate EPR dosimetry.