Basic investigation on performance of low-density polymer gel dosimeter

Pake, F.; Takavar, Abbas; Nedaie, Hassan Ali; Rad, Hamid Reza Saligheh; Eqlimi, Ehsan; Vaezzadeh, Vahid; Moghadam, M. Shojaee

doi:10.18869/acadpub.ijrr.14.4.349

Cited by 3 publications

(2 citation statements)

References 12 publications

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“…Recently, polyacrilamide gels were proposed for dosimetry and end-to-end test for MRI-linac apparatus [ 164 , 165 , 166 , 167 , 168 , 169 ]. Furthermore, a polymer hydrogel foam has been proposed as a potential three-dimensional experimental dosimeter for radiation treatment verification in low-density tissue such as the lung [ 143 , 170 , 171 , 172 , 173 , 174 ].…”

Section: Polyacrylamide Gelsmentioning

confidence: 99%

Hydrogels for Three-Dimensional Ionizing-Radiation Dosimetry

Marrale

D’Errico

2021

Gels

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Radiation-sensitive gels are among the most recent and promising developments for radiation therapy (RT) dosimetry. RT dosimetry has the twofold goal of ensuring the quality of the treatment and the radiation protection of the patient. Benchmark dosimetry for acceptance testing and commissioning of RT systems is still based on ionization chambers. However, even the smallest chambers cannot resolve the steep dose gradients of up to 30–50% per mm generated with the most advanced techniques. While a multitude of systems based, e.g., on luminescence, silicon diodes and radiochromic materials have been developed, they do not allow the truly continuous 3D dose measurements offered by radiation-sensitive gels. The gels are tissue equivalent, so they also serve as phantoms, and their response is largely independent of radiation quality and dose rate. Some of them are infused with ferrous sulfate and rely on the radiation-induced oxidation of ferrous ions to ferric ions (Fricke-gels). Other formulations consist of monomers dispersed in a gelatinous medium (Polyacrylamide gels) and rely on radiation-induced polymerization, which creates a stable polymer structure. In both gel types, irradiation causes changes in proton relaxation rates that are proportional to locally absorbed dose and can be imaged using magnetic resonance imaging (MRI). Changes in color and/or opacification of the gels also occur upon irradiation, allowing the use of optical tomography techniques. In this work, we review both Fricke and polyacrylamide gels with emphasis on their chemical and physical properties and on their applications for radiation dosimetry.

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Section: Polyacrylamide Gelsmentioning

confidence: 99%

Hydrogels for Three-Dimensional Ionizing-Radiation Dosimetry

Marrale

D’Errico

2021

Gels

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“…Conventional gel formulations are water-equivalent, so they are optimized for measuring dose to soft tissue but not to lung tissue. Previous studies have explored the development of lung-equivalent gels using two different methods to reduce the density of the gel (Ølberg et al 2000, Haraldsson et al 2006, Claeys et al 2006, De Deene et al 2006, Pak et al 2016. One technique involves beating the gel to a foam-like consistency before it sets, and the second involves mixing gel with small polystyrene beads to simulate air pockets.…”

Section: Introductionmentioning

confidence: 99%

Low-density gel dosimeter for measurement of the electron return effect in an MR-linac

McDonald

Lee

2019

Phys. Med. Biol.

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Radiation therapy in the presence of a strong magnetic field is known to cause regions of enhanced and reduced dose at interfaces of materials with varying densities, in a phenomenon known as the electron return effect (ERE). In this study, a novel low-density gel dosimeter was developed to simulate lung tissue and was used to measure the ERE at the lung-soft tissue interface. Low-density gel dosimeters were developed with Fricke xylenol orange gelatin (FXG) and ferrous oxide xylenol orange (FOX) gels mixed with polystyrene foam beads of various sizes. The gels were characterized based on CT number, MR signal intensity, and uniformity. All low-density gels had CT numbers roughly equivalent to lung tissue. The optimal lung-equivalent gel formulation was determined to be FXG with <1 mm polystyrene beads due to the higher signal intensity of FXG compared to FOX and the higher uniformity with the small beads. Dose response curves were generated for the optimal low-density gel and conventional FXG. The change in spin-lattice relaxation rate (R1) before and after irradiation was linear with dose for both gels. Next, phantoms consisting of concentric cylinders with low-density and conventional FXG were created to simulate the lung-soft tissue interface. The phantoms were irradiated in a conventional linear accelerator (linac) and in a linac combined with a 1.5 T magnetic resonance imaging (MRI) unit (MR-linac) to measure the effects of the magnetic field on the dose distribution. Hot and cold spots were observed in the dose distribution at the boundaries between the gels for the phantom irradiated in the MR-linac but not the conventional linac, consistent with the ERE.

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Evaluation of a lung-equivalent gel dosimeter for MR image-guided radiation therapy

McDonald

Ibbott

2019

J. Phys.: Conf. Ser.

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With recent advances in magnetic resonance image-guided radiation therapy (MR-IGRT), Fricke gel dosimetry has demonstrated value for its ability to measure three-dimensional dose distributions in the presence of a strong magnetic field. This strong magnetic field causes hot and cold spots in dose distributions at the interfaces of lung and normal tissue due to a phenomenon known as the electron return effect (ERE). In this paper, we report the development of lung-equivalent gel dosimeters to better measure dose to lung tissue caused by the ERE. Small polystyrene beads of variable sizes were mixed into Fricke xylenol orange gelatin (FXG) and ferrous oxide xylenol orange (FOX) gels. Lung-equivalence was confirmed by measuring the average CT number of each gel. The effects of gel type, bead size, and voxel size on uniformity and signal intensity were investigated. The smallest beads ( < 1 mm) exhibited the best uniformity, with values comparable to conventional gel with 2 mm voxels. Signal intensity followed an inverse relationship with uniformity, but FXG low-density dosimeters generated enough signal to produce acceptable quality images. The spin-lattice relaxation rate (R1 = 1/T1) increased with dose, which enabled us to measure dose to both soft tissue and lung due to the ERE using a phantom simulating the soft tissue-lung interface.

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Basic investigation on performance of low-density polymer gel dosimeter

Cited by 3 publications

References 12 publications

Hydrogels for Three-Dimensional Ionizing-Radiation Dosimetry

Hydrogels for Three-Dimensional Ionizing-Radiation Dosimetry

Low-density gel dosimeter for measurement of the electron return effect in an MR-linac

Evaluation of a lung-equivalent gel dosimeter for MR image-guided radiation therapy

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