GNP enhanced responses in microdosimetric spectra for 192Ir source

The potential radiosensitizing effects of gold nanoparticles (GNPs) in radiation therapy have been extensively studied. GNPs loaded in the tumor produce a large number of low-energy secondary electrons which contribute to the local dose enhancement and elevate the relative biological effectiveness (RBE). Thus GNP enhanced responses in 192Ir, a widely used brachytherapy source, are the subject of interest. These radiosensitizing effects can be examined through comparisons between microdosimetric spectra of secondary electrons resulting from the 192Ir in the presence and absence of GNPs in cells. Measurements of single-event lineal energy spectra give indications of a relative therapeutic advantage. In the present work, a mini tissue equivalent proportional counter (TEPC) was constructed to measure the microdosimetric spectra in cells containing and without GNPs for 192Ir source. A plug, either contained a 50 nm-thick gold foil coated on its inner surface or without the foil, was inserted into the TEPC wall during measurements. Analyses of the measured un-normalized and normalized dose lineal energy spectra provided information on the enhancements in absorbed dose and RBE. The dose enhancement was 1.27 and 1.37 for 1 and 0.5 μm-diameter sites, respectively. The increase in dose enhancement with decreasing site diameter revealed the sharp fall-off in the local dose enhancement. Applying the biological weighting function method, the RBE enhancement was 1.32 based on the lineal energy spectra of 1 μm site.