A basic study of some normoxic polymer gel dosimeters

Abstract

Polymer gel dosimeters offer a wide range of potential applications in the three-dimensional verification of complex dose distribution such as in intensity-modulated radiotherapy (IMRT). Until now, however, polymer gel dosimeters have not been widely used in the clinic. One of the reasons is that they are difficult to manufacture. As the polymerization in polymer gels is inhibited by oxygen, all free oxygen has to be removed from the gels. For several years this was achieved by bubbling nitrogen through the gel solutions and by filling the phantoms in a glove box that is perfused with nitrogen. Recently another gel formulation was proposed in which oxygen is bound in a metallo-organic complex thus removing the problem of oxygen inhibition. The proposed gel consists of methacrylic acid, gelatin, ascorbic acid, hydroquinone and copper(II)sulphate and is given the acronym MAGIC gel dosimeter. These gels are fabricated under normal atmospheric conditions and are therefore called 'normoxic' gel dosimeters. In this study, a chemical analysis on the MAGIC gel was performed. The composition of the gel was varied and its radiation response was evaluated. The role of different chemicals and the reaction kinetics are discussed. It was found that ascorbic acid alone was able to bind the oxygen and can thus be used as an anti-oxidant in a polymer gel dosimeter. It was also found that the anti-oxidants N-acetyl-cysteine and tetrakis(hydroxymethyl)phosphonium were effective in scavenging the oxygen. However, the rate of oxygen scavenging is dependent on the anti-oxidant and its concentration with tetrakis(hydroxymethyl)phosphonium being the most reactive anti-oxidants. Potentiometric oxygen measurements in solution provide an easy way to get a first impression on the rate of oxygen scavenging. It is shown that cupper(II)sulphate operates as a catalyst in the oxidation of ascorbic acid. We, therefore, propose some new normoxic gel formulations that have a less complicated chemical formulation than the MAGIC gel.

Indigenously developed multipurpose acrylic head phantom for verification of IMRT using film and gel dosimetry

“…( 9 ) MAGAT gel has the advantage over MAGIC gel in tissue equivalence and dose sensitivity. ( 10 ) Several research groups and commercial vendors are showing keen interest to establish 3D dosimetry in radiotherapy clinic. As far as IMRT is concerned, one of the key components as listed by Moran et al ( 11 ) in their study is to perform patient specific pretreatment QA.…”

MAGAT gel and EBT2 film‐based dosimetry for evaluating source plugging‐based treatment plan in Gamma Knife stereotactic radiosurgery

“…In recent times, 3D dosimetry, such as gel dosimetry, has gained popularity because it has the potential to measure highly complex treatments, which is particularly significant in situations where steep dose gradients exist such as intensity‐modulated radiation therapy (IMRT) and SRS 20 , 21 , 22 , 23 , 24 , 25 , 26 . This 3D measurement method simulates all major aspects of the treatment process, and provides 3D dose distributions measurements with high resolution.…”

3D Dosimetric Tools in Radiotherapy for Photon Beams

“…In 1992, formulations like BANANA, BANG and PAG polymer gels were proposed [25,26]. The suppression of polymerization by oxygen, present in these gels, was improved with a proposition of MAGIC gel (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper) [27], which allows the MAGIC polymeric gels to be prepared in normal weather conditions [28][29][30], which for higher temperatures beyond 25 °C loss stability. Thus, was add formaldehyde to the original formulation of the MAGIC, re-calling as MAGIC-f, which led to a rise in its melting point to 69 °C [31].…”

“…In this context, dosimetry based on gel has shown a great potential for measured dose-distribution in 3D [4][5][6][7].…”