The fundamental radiation properties of normoxic polymer gel dosimeters: a comparison between a methacrylic acid based gel and acrylamide based gels

Abstract

Polymer gel dosimeters offer a wide range of applications in the three-dimensional verification of complex dose distributions such as in intensity-modulated radiotherapy. One of the major difficulties with polymer gel dosimeters is their sensitivity to oxygen, as oxygen inhibits the radiation-induced polymerization reaction. For several years, oxygen was removed from the gels by bubbling the sol with inert gases for several hours during the gel fabrication. Also, the gel had to be poured in containers with low oxygen permeability and solubility. Recently, it was found that these technical difficulties can easily be solved by adding an antioxidant to the gel. These gels are called 'normoxic' gels as they can be produced under normal atmospheric conditions. In this study several properties of polymer gel dosimeters have been investigated: the dose sensitivity, the temporal and spatial stability of the gel, the sensitivity of the dose response to temperature during irradiation and during MR imaging, the energy dependence and the dose-rate dependence. This study reveals that the normoxic polymer gel dosimeter based on methacrylic acid (nMAG) studied in this work has inferior radiation properties as compared to the polyacrylamide gelatine (PAG) gel dosimeters. It is shown that from the three different gel dosimeters investigated in this study, the nPAG gel dosimeter results in a less sensitive gel dosimeter but with superior radiation properties as compared to the nMAG gel dosimeter. The importance of investigating relevant radiation properties of gel dosimeters apart from the radiation sensitivity-prior to their use for dosimetric validation experiments-is illustrated and emphasized throughout this study. Other combinations of monomer and gelling agent may result in more reliable normoxic polymer gel dosimeters.

Optimisation of the MAGAT gel dosimeter compositions

“…An increase in monomer concentration in a polymer gel dosimeter increases the sensitivity (15)(16)(17) as can be seen in the results of the present study presented in igure 7. The sensitivity increment of the MAGAT gel dosimeter depends on the MAA concentration.…”

Polymer gel dosimetry of an electron beam in the presence of a magnetic field

“…The polymer gel was fabricated according to a procedure as described elsewhere [5]. The gel was at 32 °C when it was poured in 21 test tubes and two Barex™ containers (20 x 20 x 6 cm³).…”

Measurement of a PAGAT gel dosimeter by ultrasound computed tomography

“…Following irradiation, the physical properties of these radiosensitive gels undergo changes that can be measured using various medical imaging equipment . Traditionally this imaging has utilised either optical computed tomography (CT) [1,2] magnetic resonance imaging [3][4][5] or x-ray CT [6,7]. Previous studies have examined the feasibility of ultrasound based CT to study dose response in PAG dosimeters [8][9][10][11].…”