New application of polymer gels in medical radiation dosimetry: Plasmonic sensors

Polymer gels are amongst the most promising future dosimetric tools for medical applications, since irradiated gels are capable to represent a phantom and a dosimeter with a 3D-dose distribution measurement capability and biological tissue equivalency in one. High spatial resolution of these gels but limited dose sensitivity, especially in low dose region, as well complicated and time consuming read out methods are the main issues needing improvement. Operating principle of plasmonic sensors which are commonly used in biotechnology to assess the concentration and reaction rate of various organic compounds, is based on the excitation of strong free electron oscillations (surface plasmon resonance, SPR) in the boundary layer between metal and dielectric using polarized light and measurement of the refracted light characteristics. Plasmonic sensors stand out from the other sensing technologies due to their high resolution and relatively low uncertainties. Combination of plasmonic sensors' characteristics and capabilities of dosimetric gels is key when developing dosimetric gel based SPR sensors for point dose measurements and corresponding relatively simple, however sensitive, in-house made dosimetric system working in angular mode, all of which is presented in this paper. Developed plasmonic sensor itself comprised out of Au diffraction grating, extracted from commercial optical media disc, spin-coated with a thin dosimetric gel (nPAG or VIPET) layer. Fabrication procedure of the plasmonic sensor and creation of the corresponding optical read out system are discussed in this paper. Irradiation experiments performed with dosimetric gel based SPR sensor (point dosimeter) have shown the feasibility of this new type dosimetry system to measure low absorbed doses (up to 5Gy) and revealed the potential of this system to perform measurements with the dosimetric sensitivity up to two times higher as compared to other known optical dose evaluation methods. Key aspects regarding sensitivity and resolution of plasmonic dosimeters are also discussed.