Polymer gel dosimetry of added High-Z elements in radiation fields of electrons and photons with low and high photon energy

A dose enhancement in tumors can in principle be achieved using an enrichment of elements with high atomic number (“High-Z therapy”). The proof of dose enhancement at low non-toxic concentrations remains difficult with standard dosimeters due to the small distance of secondary electrons of X-ray photon energies. We investigated within an exploratory research approach the dose enhancement in tissue equivalent environment using MRI analysis of polymer gel dosimeters doped with molecules containing high-Z elements: bismuth, silver iodide and iopromide, a radio-diagnostic contrast agent for X-ray imaging, in photon fields of low (200 kV X-ray) and high energy (6 MV) and in an electron field (6 MeV). An enhancement of the dose response up to a relative dose enhancement factor rDE exp ≌1.4 was observed for low concentrations (w/w=0.006) of iopromide, already approved for vascular angiography with X-rays. Experimental limitations and challenging interpretations are outlined.