Polymer gel water equivalence and relative energy response with emphasis on low photon energy dosimetry in brachytherapy

Abstract

The water equivalence and stable relative energy response of polymer gel dosimeters are usually taken for granted in the relatively high x-ray energy range of external beam radiotherapy based on qualitative indices such as mass and electron density and effective atomic number. However, these favourable dosimetric characteristics are questionable in the energy range of interest to brachytherapy especially in the case of lower energy photon sources such as 103Pd and 125I that are currently utilized. In this work, six representative polymer gel formulations as well as the most commonly used experimental set-up of a LiF TLD detector-solid water phantom are discussed on the basis of mass attenuation and energy absorption coefficients calculated in the energy range of 10 keV-10 MeV with regard to their water equivalence as a phantom and detector material. The discussion is also supported by Monte Carlo simulation results. It is found that water equivalence of polymer gel dosimeters is sustained for photon energies down to about 60 keV and no corrections are needed for polymer gel dosimetry of 169Yb or 192Ir sources. For 125I and 103Pd sources, however, a correction that is source-distance dependent is required. Appropriate Monte Carlo results show that at the dosimetric reference distance of 1 cm from a source, these corrections are of the order of 3% for 125I and 2% for 103Pd. These have to be compared with corresponding corrections of up to 35% for 125I and 103Pd and up to 15% even for the 169Yb energies for the experimental set-up of the LiF TLD detector-solid water phantom.

Water equivalence of polymer gel dosimeters

“…The photon mass attenuation coefficient (m=r), photon mass energy absorption coefficient (m en =r) (Venning et al, 2005a,b;De Deene et al, 2006;Pantelis et al, 2004) and total stopping power ðS=rÞ tot of electrons are the basic quantities used in calculation of penetration and energy deposition by the photons and electrons. All calculations were done using the XCOM and the ESTAR database which are available online (http://physics.nist.…”

Evaluation of MRI-based MAGIC polymer gel dosimeter in small photon fields

“…These dosimeters don't perturb radiation ield because the material phantom and these detector are the same (10) . Because of these bene its several studies in radiation small ields have been accomplished by using several types of polymer gel dosimeter (3,7,(11)(12)(13)(14) but the MRI-based on MAGIC polymer gel dosimeter has not been evaluated for small ields.…”

Efficiency corrections in determining the 137Cs inventory of environmental soil samples by using relative measurement method and GEANT4 simulations

“…The Z eff is a useful tool to account absorption for gamma-rays (especially for lower photon energies), because the increasing Z eff corresponds to the increasing photon reaction cross section (Dziri et al, 2014). The Z eff of the soil mixture can be calculated using the following equations (Jones et al, 2003;Pantelis et al, 2004):…”