MO-F-213AB-06: Experimental Evaluation of Radiation Dose Effect by High Atomic Number Materials for Superficial Radiation Therapy

High atomic number (Z) materials have been considered as a method for enhancing radiation dose in tumors. The dose enhancement due to interactions of kilovoltage x-rays with high-Z materials (i.e., gold or iodine) has been well demonstrated through computational works. This study is to experimentally quantify the effect using gold nanoparticles (AuNPs) and iodine solutions, respectively.

Iodine and AuNPs (AuroVist, Nanoprobes, Yaphank NY) are uniformly distributed in each cylinder phantom (1.6 cm diameter and 2.0 cm depth) separately. Concentrations of Iodine and AuNPs were varied from 40 to 225 mg/ml and 16.0 mg/ml to 42.7 mg/ml, respectively. The Iodine solutions were irradiated with 75 to 150 kVp x-rays from a superficial x-ray therapy machine at doses of 250 to 400 cGy. The AuNPs solutions in the cylinder were irradiated with 40 to 150 kVp x-rays. The phantom was placed at the center of the cone to ensure a uniform radiation field. Radiation doses were measured using GafChromic EBT2 films (International Specialty Products, Wayne NJ). Dose enhancement factors (DEF), i.e., the ratio of dose to high-Z material versus dose to water, were calculated and plotted as functions of concentration and kVp.

Experimental DEFs varied between 1.01 and 1.38. The DEFs increased with increasing concentration and varied with changing kVp. The maximum DEF measured for Iodine solution was 1.38 at 225 mg/ml and 150 kVp. The maximum DEF measured for AuNPs was 1.22 at 42.7 mg/ml and 40 kVp. The target volume covered by dose enhancement is larger with relatively lower concentrations.

The magnitude of dose enhancement due to AuNPs and Iodine presence has a dependency with the concentration and kVp. In clinical applications, the concentration of the high-Z material and kVp should also be selected to suit the depth and volume of the target tumor.