Polymer gels for magnetic resonance imaging of radiation dose distributions at normal room atmosphere

Abstract

Polymer gels whose NMR and optical properties change when irradiated offer unique advantages for measuring radiation dose distributions. To date, all acrylic polymer gel dosimeters must be manufactured, stored and irradiated in hypoxic conditions which severely limits their use and stability. A new formulation of acrylic dosimeter gel has been developed that responds well in normal atmosphere and which we have named MAGIC (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper). To produce dosimeter gels, an aqueous solution of gelatin, open to the atmosphere, is mixed with methacrylic acid, copper(II) ions, ascorbic acid and hydroquinone. It is believed that the copper(II) and ascorbic acid form a complex with oxygen which (with radiolysis of water) serves as a free radical source for the initiation of the polymerization of methacrylic acid. At room air the water proton spin relaxation rate R2 in MAGIC gels is proportional to absorbed dose though the precise relationship depends on the composition of the gel and the initiating complex. For example, in the range 0-30 Gy the slope of the response of R2 versus dose at 20 MHz was 0.300, 0.519 and 0.681 s(-1) Gy(-1), respectively, when the concentration of MAA was 3, 6 and 9%. The slopes increased to 0.310, 0.567 and 0.868 s(-1) Gy(-1) at 85 MHz. An important determinant of the sensitivity to detect small dose changes is shown to be the slope-to-intercept ratio of the dose-response curve. These varied from 0.08 to 0.17, comparable to hypoxic gels described earlier. MAGIC gels can be manufactured and used much more easily than the previous formulations and can be imaged by magnetic resonance imaging or optical scanning, and thus they will likely be of considerable interest to radiation physicists.

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

“…Finally tetrakis(hydroxymethyl)phosphonium chloride (THPC) was added to the gel composition by bringing down the temperature to 20°C. ( 9 , 15 , 16 ) The prepared gel was poured in to three cylindrical gel inserts which were used for IMRT plan verification and into small gel vials or tubes (see Table 1). …”

“…MAGAT gel was used for this 3D verification study, which is a modified version of the first normoxic polymer gel named MAGIC gel. ( 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.…”

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

“…MAGIC gel was used for 3D dose verification in radiosurgery previously by several authors 3 , 27 , 28 . MAGAT gel, which is a modified version of MAGIC gel, was not tested for radiosurgery verification.…”

MAGIC polymer gel for dosimetric verification in boron neutron capture therapy

“…The gel was prepared in normal room atmosphere in a fume cupboard using the gel preparation method described by Fong et al (24) The chosen MAGIC gel composition was previously used and characterized by Gustavsson et al ( 25 , 26 ) Table 1 shows the composition.…”

“…( 2 , 23 ) Polymer gel dosimeters known by the acronym MAGIC (methacrylic and ascorbic acid in gelatin initiated by copper) can be prepared in normal‐room atmosphere more easily and faster than BANG‐type gel. ( 24 , 25 ) …”