Characterization of novel water-equivalent PRESAGE® dosimeters for megavoltage and kilovoltage x-ray beam dosimetry

Abstract

In this paper we introduce three novel PRESAGE® dosimeters referred to as metal optimized dosimeters (MODs) 1, 2 and 3, and determine their sensitivity, as well as their water equivalency. All three formulations contained very small concentrations (0.01 wt%) of metal compounds. The radiological properties were key factors that were considered when designing and formulating the new dosimeters. The dosimeters were prepared in spectrophotometric cuvettes, irradiated with a 6 MV X-ray beam, and the change in optical density of each dosimeter was measured using a spectrophotometer. Results show that all three MOD formulations exhibit radiological properties closer to water than the recently introduced PRESAGE® dosimeter formulation referred to as formulation A, with mass densities of the novel formulations varying by only 3.9% from that of water, as compared to 5.3% for the commercial formulation. Whereas the novel formulations have almost identical Zeff values to that of water (Zeff = 7.42), the Zeff for the commercial formulation was 3.7% higher than that of water. Comparison of mass energy coefficients for all MOD formulations showed a maximum variation of approximately 0.6 times closer to water especially MOD 3 whereas commercial formulation was 1.23 times larger than water at approximately 40 keV. The same effect was observed for mass attenuation coefficients comparison. MOD 3 was also more sensitive to radiation than MOD 1 and 2 as a result of the inclusion of bromine-based halocarbons in the formulation. All novel MOD formulations were comparable to commercial formulation in terms of probability of Compton scatter and pair production compared to water. However, the probability of photoelectric absorption in the three novel MOD formulations varied significantly less (1.3 times greater) from that of water as compared to the commercial formulation (1.8 times greater). Given that all three novel MOD formulations displayed improved radiological properties over any of the currently available PRESAGE® dosimeter formulations makes them ideal candidates for tissue mimics in dosimetry of clinical megavoltage and kilovoltage x-ray beams.