An evaluation of epoxy resin phantom materials for megavoltage photon dosimetry

Abstract

Epoxy resin phantom materials have been available for some time and are widely used for dosimetry purposes, not least in audit phantoms. Information on their behaviour is partly available in the literature, but there are different mixes and formulations often given similar names and it may not be appropriate to transfer information from one material to another. Five commercially available water substitute materials have been evaluated for use in megavoltage photon beams: WT1, WTe, RMI 451, RMI 457 and 'plastic water'. Four independent experiments were carried out to compare these materials with water in megavoltage photon beams ranging in energy from cobalt 60 to nominal 16 MV x-rays, and some general conclusions are drawn from the results as to their use. All are suitable for relative dosimetry in megavoltage photon beams. However, differences of up to 1% are observed for absolute measurements. The newer formulations, developed for electron beam use, are also closer to water for megavoltage photon beams.

Evaluation of the water equivalence of solid phantoms using gamma ray transmission measurements

“…The agreement was in most cases within 1% and a maximum deviation of 1.5%. This level of agreement between doses measured in solid phantoms and in water is similar to previous work using megavoltage X-ray beams (Allahverdi et al, 1999;Liu et al, 2003) and in Monte Carlo calculations at similar photon energies for brachytherapy sources (Meigooni et al, 1994). The transmission values through Perspex are less than those for water and with a greater deviation, being up to 4% at depth.…”

“…One aspect of the solid phantoms that will contribute to uncertainties in the transmission measurements is the inhomogeneity in the manufacture of the blocks, leading to variations in density (Allahverdi et al, 1999;Seuntjens et al, 2005). The results indicate that within the uncertainties, the Plastic Water, RMI-457 Solid Water and RW3 phantom materials meet the ICRU requirements for water equivalency at this particular energy.…”

“…Testing the radiological tissue equivalence in terms of the water equivalency of a solid phantom for X-rays with lower energies can be achieved by several methods: measurement of relative dosimetry data such as percentage depth doses and output factors (Allahverdi et al, 1999;Healy et al, 2005;Hill et al, 2005), measurement of X-ray beam attenuation and/or back scatter factors (Hermann et al, 1985), measurement of X-ray linear attenuation coefficient, , using radioisotopes (Midgley, 2005) and Monte Carlo dose calculations (Meigooni et al, 1994;Reniers et al, 2004).…”

Dosimetric evaluation of a MOSFET detector for clinical application in photon therapy

“…1b). Here, Allahverdi et al [9] reported that the SW phantom is suitable for relative dosimetry in megavoltage photon beams, and difference of up to 1% is observed for absolute measurements. For angular dependence measurements, we used a cylindrical PMMA phantom with a radius of 8.0 cm as shown in Fig.…”

Use of a megavoltage electronic portal imaging device to identify prosthetic materials

“…When commissioned in a 6 MV photon beam, the percent depth dose measured with an ionisation chamber was compared to measurements in water and a maximum difference of 1.1 % was observed at a depth of 26 cm. More rigorous testing by Tello et al [17] and Allahverdi et al [18] have quantified agreement at this beam quality to within 0.5 %.…”