Water equivalency evaluation of PRESAGE<sup>®</sup>dosimeters for dosimetry of Cs-137 and Ir-192 brachytherapy sources

Gorjiara, Tina; Hill, Robin; Kuncic, Zdenka; Baldock, Clive

doi:10.1088/1742-6596/250/1/012093

Cited by 10 publications

(12 citation statements)

References 10 publications

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“…8 This system has been used extensively for external beam radiotherapy 1,2 and in a few cases, to measure the dose distribution about a brachytherapy source. 10,11 Verification of the attenuation characteristics of brachytherapy applicators is a natural extension of previously reported applications of the PRESAGE/DLOS 3D dosimetry system.…”

Section: Introductionmentioning

confidence: 90%

“…10,26 In addition to this, we evaluated the PRESAGE/DLOS system for measurements of 137 Cs by first measuring the 3D dose distribution about an unshielded source, after which the distribution was measured about sources placed within the attenuating buckets. Cylindrical polymer based PRESAGE dosimeters 1,2,21 (9.5 cm diameter, 9.2 cm height) were manufactured.…”

Section: Iib2 3d Dosimetrymentioning

confidence: 99%

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Commissioning a CT-compatible LDR tandem and ovoid applicator using Monte Carlo calculation and 3D dosimetry

et al. 2012

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Purpose: To determine the geometric and dose attenuation characteristics of a new commercially available CT-compatible LDR tandem and ovoid (T&O) applicator using Monte Carlo calculation and 3D dosimetry. Methods: For geometric characterization, we quantified physical dimensions and investigated a systematic difference found to exist between nominal ovoid angle and the angle at which the afterloading buckets fall within the ovoid. For dosimetric characterization, we determined source attenuation through asymmetric gold shielding in the buckets using Monte Carlo simulations and 3D dosimetry. Monte Carlo code MCNP5 was used to simulate 1.5 × 10 9 photon histories from a 137 Cs source placed in the bucket to achieve statistical uncertainty of 1% at a 6 cm distance. For 3D dosimetry, the distribution about an unshielded source was first measured to evaluate the system for 137 Cs, after which the distribution was measured about sources placed in each bucket. Cylindrical PRESAGE R dosimeters (9.5 cm diameter, 9.2 cm height) with a central channel bored for source placement were supplied by Heuris Inc. The dosimeters were scanned with the Duke Large field of view Optical CT-Scanner before and after delivering a nominal dose at 1 cm of 5-8 Gy. During irradiation the dosimeter was placed in a water phantom to provide backscatter. Optical CT scan time lasted 15 min during which 720 projections were acquired at 0.5• increments, and a 3D distribution was reconstructed with a (0.05 cm) 3 isotropic voxel size. The distributions about the buckets were used to calculate a 3D distribution of transmission rate through the bucket, which was applied to a clinical CT-based T&O implant plan. Results: The systematic difference in bucket angle relative to the nominal ovoid angle (105 • ) was 3.1• -4.7• . A systematic difference in bucket angle of 1 • , 5• , and 10• caused a 1% ± 0.1%, 1.7% ± 0.4%, and 2.6% ± 0.7% increase in rectal dose, respectively, with smaller effect to dose to Point A, bladder, sigmoid, and bowel. For 3D dosimetry, 90.6% of voxels had a 3D γ -index (criteria = 0.1 cm, 3% local signal) below 1.0 when comparing measured and expected dose about the unshielded source. Dose transmission through the gold shielding at a radial distance of 1 cm was 85.9% ± 0.2%, 83.4% ± 0.7%, and 82.5% ± 2.2% for Monte Carlo, and measurement for left and right buckets, respectively. Dose transmission was lowest at oblique angles from the bucket with a minimum of 56.7% ± 0.8%, 65.6% ± 1.7%, and 57.5% ± 1.6%, respectively. For a clinical T&O plan, attenuation from the buckets leads to a decrease in average Point A dose of ∼3.2% and decrease in D 2cc to bladder, rectum, bowel, and sigmoid of 5%, 18%, 6%, and 12%, respectively. Conclusions: Differences between dummy and afterloading bucket position in the ovoids is minor compared to effects from asymmetric ovoid shielding, for which rectal dose is most affected. 3D dosimetry can fulfill a novel role in verifying Monte Carlo calculations of complex dose distributions as are common about brachy...

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Section: Introductionmentioning

confidence: 90%

Section: Iib2 3d Dosimetrymentioning

confidence: 99%

Commissioning a CT-compatible LDR tandem and ovoid applicator using Monte Carlo calculation and 3D dosimetry

et al. 2012

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“…15,16 These attributes are especially important for brachytherapy measurements with high dose gradients and requiring source placement within the dosimeter via a channel. 17 PRESAGE R has already been applied to measure the dose distribution surrounding cesium-137 and iridium-192 brachytherapy sources [18][19][20] in conjunction with the Duke Large field of view optical CT-scanner (DLOS). 17,21 Recent advances in 3D dosimetry technology have potential to make feasible dose measurements surrounding low energy sources as well.…”

Section: Presagementioning

confidence: 99%

“…25 Water equivalence of some formulations has been evaluated for various photon and particle beam energies, 18,26 but has yet to be quantified for low energy brachytherapy sources. 2.…”

Section: Water Equivalency Of Polyurethane Dosimeters For Lowmentioning

confidence: 99%

On the feasibility of polyurethane based 3D dosimeters with optical CT for dosimetric verification of low energy photon brachytherapy seeds

et al. 2014

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Purpose:To investigate the feasibility of and challenges yet to be addressed to measure dose from low energy (effective energy <50 keV) brachytherapy sources (Pd-103, Cs-131, and I-125) using polyurethane based 3D dosimeters with optical CT. Methods: The authors' evaluation used the following sources: models 200 (Pd-103), CS-1 Rev2 (Cs-131), and 6711 (I-125). The authors used the Monte Carlo radiation transport code MCNP5, simulations with the ScanSim optical tomography simulation software, and experimental measurements with PRESAGE R dosimeters/optical CT to investigate the following: (1) the water equivalency of conventional (density = 1.065 g/cm 3 ) and deformable (density = 1.02 g/cm 3 ) formulations of polyurethane dosimeters, (2) the scatter conditions necessary to achieve accurate dosimetry for low energy photon seeds, (3) the change in photon energy spectrum within the dosimeter as a function of distance from the source in order to determine potential energy sensitivity effects, (4) the optimal delivered dose to balance optical transmission (per projection) with signal to noise ratio in the reconstructed dose distribution, and (5) the magnitude and characteristics of artifacts due to the presence of a channel in the dosimeter. Monte Carlo simulations were performed using both conventional and deformable dosimeter formulations. For verification, 2.8 Gy at 1 cm was delivered in 92 h using an I-125 source to a PRESAGE R dosimeter with conventional formulation and a central channel with 0.0425 cm radius for source placement. The dose distribution was reconstructed with 0.02 and 0.04 cm 3 voxel size using the Duke midsized optical CT scanner (DMOS). Results: While the conventional formulation overattenuates dose from all three sources compared to water, the current deformable formulation has nearly water equivalent attenuation properties for Cs-131 and I-125, while underattenuating for Pd-103. The energy spectrum of each source is relatively stable within the first 5 cm especially for I-125. The inherent assumption of radial symmetry in the TG43 geometry leads to a linear increase in sample points within the 3D dosimeter as a function of distance away from the source, which partially offsets the decreasing signal. Simulations of dose reconstruction using optical CT showed the feasibility of reconstructing dose out to a radius of 10 cm without saturating projection images using an optimal dose and high dynamic range scanning; the simulations also predicted that reconstruction artifacts at the channel surface due to a small discrepancy in refractive index should be negligible. Agreement of the measured with calculated radial dose function for I-125 was within 5% between 0.3 and 2.5 cm from the source, and the median difference of measured from calculated anisotropy function was within 5% between 0.3 and 2.0 cm from the source. Conclusions: 3D dosimetry using polyurethane dosimeters with optical CT looks to be a promising application to verify dosimetric distributions surrounding low energy brachytherapy sources.

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“…The radiological properties including effective atomic number, number of electrons per gram, mass density and electron density should be same as radiological properties of water or tissue [7,8]. Several studies have been done to investigate water equivalency of different polymer gel dosimetry for photon and electron beam dosimetry [1,[9][10][11][12][13][14][15][16][17][18]. MAGIC gel dosimeter has previously been investigated for its radiological interaction properties and radiological water equivalence [1,10].…”

Section: Introductionmentioning

confidence: 99%

Radiological properties of MAGIC normoxic polymer gel dosimetry

Aljamal¹,

Zakaria²,

Shamsuddin

2013

J. Phys.: Conf. Ser.

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Radiological characterization and water equivalency of genipin gel for x-ray and electron beam dosimetry Tina Gorjiara, Robin Hill, Zdenka Kuncic et al. Abstract. For a polymer gel dosimeter to be of use in radiation dosimetry, it should display water-equivalent radiological properties. In this study, the radiological properties of the MAGIC (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper) normoxic polymer gels were investigated. The mass density ( ) was determined based on Archimedes principle. The weight fraction of elemental composition and the effective atomic number (Z eff ) were calculated. The electron density was also measured with 90° scattering angle at room temperature. The linear attenuation coefficient (µ) of unirradiated gel, irradiated gel, and water were determined using Am-241 based on narrow beam geometry. Monte Carlo simulation was used to calculate the depth doses response of MAGIC gel and water for 6MV photon beam. The weight fractions of elements composition of MAGIC gel were close to that for water. The mass density was found to be 1027 ± 2 kg m 3 , which is also very close to mass density of muscle tissue (1030 kg m 3 ) and 2.7% higher than that of water. The electron density ( e ) and atomic number (Z eff ) were found to be 3.43 × 10 29 e m 3 and 7.105, respectively. The electron density measured was 2.6% greater than that for water. The atomic number was very close to that for water. The prepared MAGIC gel was found to be water equivalent based on the study of element composition, mass density, electron density and atomic number. The linear attenuation coefficient of unirradiated gel was very close to that of water. The µ of irradiated gel was found to be linear with dose 2-40 Gy. The depth dose response for MAGIC gel from a 6 MV photon beam had a percentage dose difference to water of less than 1%. Therefore it satisfies the criteria to be a good polymer gel dosimeter for radiotherapy.

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Water equivalency evaluation of PRESAGE^®dosimeters for dosimetry of Cs-137 and Ir-192 brachytherapy sources

Cited by 10 publications

References 10 publications

Commissioning a CT-compatible LDR tandem and ovoid applicator using Monte Carlo calculation and 3D dosimetry

Commissioning a CT-compatible LDR tandem and ovoid applicator using Monte Carlo calculation and 3D dosimetry

On the feasibility of polyurethane based 3D dosimeters with optical CT for dosimetric verification of low energy photon brachytherapy seeds

Radiological properties of MAGIC normoxic polymer gel dosimetry

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Water equivalency evaluation of PRESAGE®dosimeters for dosimetry of Cs-137 and Ir-192 brachytherapy sources

Cited by 10 publications

References 10 publications

Commissioning a CT-compatible LDR tandem and ovoid applicator using Monte Carlo calculation and 3D dosimetry

Commissioning a CT-compatible LDR tandem and ovoid applicator using Monte Carlo calculation and 3D dosimetry

On the feasibility of polyurethane based 3D dosimeters with optical CT for dosimetric verification of low energy photon brachytherapy seeds

Radiological properties of MAGIC normoxic polymer gel dosimetry

Contact Info

Product

Resources

About

Water equivalency evaluation of PRESAGE^®dosimeters for dosimetry of Cs-137 and Ir-192 brachytherapy sources