Determination of the Absorbed Dose Rate to Water for the 18-mm Helmet of a Gamma Knife

Chung, Hyun‐Tai; Hyun, Sangil; Choi, Yongsoo; Kim, Gi Hong; Kim, Dong Gyu; Chun, Kook Jin

doi:10.1016/j.ijrobp.2010.05.039

Cited by 8 publications

(12 citation statements)

References 10 publications

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“…The offsets of the mechanical center from the radiological center of the calibration films were −0.1 ± 0.1 mm along the x ‐axis and −0.2 ± 0.1 mm along the y ‐axis. The calculated dose at this mechanical center was set to 98.5% of the LGP maximum dose because this point was approximately 3.5 mm from the dose‐maximum point along the z‐axis . The mean OD value of the three films irradiated to a calibration dose was employed as the measured OD value of that dose.…”

Section: Resultsmentioning

confidence: 99%

“…For example, virtual target plans at the ‘top’ showed substantially better GIPR values of 99.4 ± 0.7% and NATI values of 0.6 ± 0.5 when we employed the slice that was 0.6 mm below the center slice of the computed dose. Third, the uncertainty in depth has a greater effect on the dose‐rate calculation of the convolution algorithm in a peripheral region than the uncertainty in depth in a central region because the dose rate exponentially decreases in a head . Thus, the same uncertainty in depth produces a larger change in the dose rate at the ‘top’ position than the same uncertainty in depth at the ‘bottom’ or ‘middle’ position.…”

Section: Discussionmentioning

confidence: 99%

“…The absorbed dose rate measured inside a plastic phantom is passed to the LGP and used as the absorbed dose rate in water without any correction. The errors from this substitution have been analyzed, and some alternatives were suggested …”

Section: Introductionmentioning

confidence: 99%

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Verification of dose profiles generated by the convolution algorithm of the gamma knife^® radiosurgery planning system

2017

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The measured accuracies of the dose distributions calculated by the convolution algorithm of the LGP were within the clinically acceptable range (GIPR ≥ 96.9%) for various configurations of collimator size, location, direction of calculation plane, and number of shots. Due to the intrinsic asymmetry in the dose distribution along the z-axis, the treatment plan should also be verified in coronal or sagittal plane.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Verification of dose profiles generated by the convolution algorithm of the gamma knife^® radiosurgery planning system

2017

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“…2b) and used as a reference value. The structure and material of the spherical water-filled phantom were described in detail in a previous report [4]. For the comparison, the commercial solid water phantom (Elekta, Sweden) was also used for measurement of the dose rate (Fig.…”

Section: Methodsmentioning

confidence: 99%

“…Although the different radiological characteristics between the plastic phantom and the water phantom must be carefully taken into account, they are neglected in most instances. In order to overcome this factor, the authors developed a spherical water-filled phantom with an equivalent water depth (EWD) of 8 g/cm 2 and showed that there could be approximately a 2% difference in dose rates measured by the spherical water-filled phantom and two ABS phantoms [4]. Although it is expected that the spherical water-filled phantom provides a more accurate value of the absorbed dose rate to water, there are practical obstacles for using this kind of phantom in ordinary clinical settings due to difficulties in management and risk of damage at the center of the GK during measurement.…”

Section: Introductionmentioning

confidence: 99%

Development of a PMMA phantom as a practical alternative for quality control of gamma knife® dosimetry

et al. 2018

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BackgroundTo measure the absorbed dose rate to water and penumbra of a Gamma Knife® (GK) using a polymethyl metacrylate (PMMA) phantom.MethodsA multi-purpose PMMA phantom was developed to measure the absorbed dose rate to water and the dose distribution of a GK. The phantom consists of a hemispherical outer phantom, one exchangeable cylindrical chamber-hosting inner phantom, and two film-hosting inner phantoms. The radius of the phantom was determined considering the electron density of the PMMA such that it corresponds to 8 g/cm2 water depth, which is the reference depth of the absorbed dose measurement of GK. The absorbed dose rate to water was measured with a PTW TN31010 chamber, and the dose distributions were measured with radiochromic films at the calibration center of a patient positioning system of a GK Perfexion. A spherical water-filled phantom with the same water equivalent depth was constructed as a reference phantom. The dose rate to water and dose distributions at the center of a circular field delimited by a 16-mm collimator were measured with the PMMA phantom at six GK Perfexion sites.ResultsThe radius of the PMMA phantom was determined to be 6.93 cm, corresponding to equivalent water depth of 8 g/cm2. The absorbed dose rate to water was measured with the PMMA phantom, the spherical water-filled phantom and a commercial solid water phantom. The measured dose rate with the PMMA phantom was 1.2% and 1.8% higher than those measured with the spherical water-filled phantom and the solid water phantom, respectively. These differences can be explained by the scattered photon contribution of PMMA off incoming 60Co gamma-rays to the dose rate. The average full width half maximum and penumbra values measured with the PMMA phantom showed reasonable agreement with two calculated values, one at the center of the PMMA phantom (LGP6.93) and other at the center of a water sphere with a radius of 8 cm (LGP8.0) given by Leksell Gamma Plan using the TMR10 algorithm.ConclusionsA PMMA phantom constructed in this study to measure the absorbed dose rates to water and dose distributions of a GK represents an acceptable and practical alternative for GK dosimetry considering its cost-effectiveness and ease of handling.

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Assessment of the accuracy and stability of frameless gamma knife radiosurgery

Chung

Park

Kim

et al. 2018

J Applied Clin Med Phys

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The aim of this study was to assess the accuracy and stability of frameless gamma knife radiosurgery (GKRS). The accuracies of the radiation isocenter and patient couch movement were evaluated by film dosimetry with a half‐year cycle. Radiation isocenter assessment with a diode detector and cone‐beam computed tomography (CBCT) image accuracy tests were performed daily with a vendor‐provided tool for one and a half years after installation. CBCT image quality was examined twice a month with a phantom. The accuracy of image coregistration using CBCT images was studied using magnetic resonance (MR) and computed tomography (CT) images of another phantom. The overall positional accuracy was measured in whole procedure tests using film dosimetry with an anthropomorphic phantom. The positional errors of the radiation isocenter at the center and at an extreme position were both less than 0.1 mm. The three‐dimensional deviation of the CBCT coordinate system was stable for one and a half years (mean 0.04 ± 0.02 mm). Image coregistration revealed a difference of 0.2 ± 0.1 mm between CT and CBCT images and a deviation of 0.4 ± 0.2 mm between MR and CBCT images. The whole procedure test of the positional accuracy of the mask‐based irradiation revealed an accuracy of 0.5 ± 0.6 mm. The radiation isocenter accuracy, patient couch movement accuracy, and Gamma Knife Icon CBCT accuracy were all approximately 0.1 mm and were stable for one and a half years. The coordinate system assigned to MR images through coregistration was more accurate than the system defined by fiducial markers. Possible patient motion during irradiation should be considered when evaluating the overall accuracy of frameless GKRS.

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Determination of the Absorbed Dose Rate to Water for the 18-mm Helmet of a Gamma Knife

Cited by 8 publications

References 10 publications

Verification of dose profiles generated by the convolution algorithm of the gamma knife^® radiosurgery planning system

Verification of dose profiles generated by the convolution algorithm of the gamma knife^® radiosurgery planning system

Development of a PMMA phantom as a practical alternative for quality control of gamma knife® dosimetry

Assessment of the accuracy and stability of frameless gamma knife radiosurgery

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Determination of the Absorbed Dose Rate to Water for the 18-mm Helmet of a Gamma Knife

Cited by 8 publications

References 10 publications

Verification of dose profiles generated by the convolution algorithm of the gamma knife® radiosurgery planning system

Verification of dose profiles generated by the convolution algorithm of the gamma knife® radiosurgery planning system

Development of a PMMA phantom as a practical alternative for quality control of gamma knife® dosimetry

Assessment of the accuracy and stability of frameless gamma knife radiosurgery

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Product

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Verification of dose profiles generated by the convolution algorithm of the gamma knife^® radiosurgery planning system

Verification of dose profiles generated by the convolution algorithm of the gamma knife^® radiosurgery planning system