Monte Carlo study of microdosimetric spectra conversion from diamond to tissue in proton therapy

Abstract

Diamond is regarded as a promising material in microdosimetry. However, since the stopping power of the diamond is different from tissue, the energy deposition distribution in the diamond is not identical to that in tissue. Therefore, a conversion of the spectra in the diamond microdosimeter to the tissue site is needed. In this work, we introduced a method for the tissue equivalence conversion of diamond microdosimeters, which is developed to perform the energy deposition spectra conversion from the diamond to an equivalent size of tissue in radiotherapy. It was derived from the scaled Fourier transformation and the scaling factor. The method was tested by comparing the spectra converted from the diamond to tissue with those obtained in tissue along the Bragg curve at different locations. The results show that: i) the conversion method can overcome the defect of poor coincidence of the spectra between converted and actual results in low deposition energy zones, which is introduced by the method derived based on the distribution characteristics; ii) The equivalence between detector material and target tissue can affect the conversion results at the plateau of the Bragg curve; iii) The inconsistency between the converted and actual spectra due to the spectra shapes was also found, which occurs in the range of η from 0.117 to 1.248 for diamonds in this work; iv) the conversion at the distal part of the Bragg peak should pay attention to the range of the incident particles and the diamond microdosimeter size. To sum up, the method introduced in this work shows relatively good results in microdosimetric spectra conversion from diamond to tissue, especially in low-energy deposition regions. Nonetheless, further study is necessary to improve the practicability of this method so that it can be competent for spectral conversion on the whole Bragg curve.