Feasibility of isodose‐shaped scintillation detectors for the measurement of gamma knife output factors

Kim, Tae Hoon; Yang, Hye Jeong; Jeong, Jae Young; Schaarschmidt, Thomas; Kim, Yong Kyun; Chung, Hyun‐Tai

doi:10.1002/mp.15469

Cited by 3 publications

(4 citation statements)

References 25 publications

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“…The effects of the deviation of the radiation focus from the UCP were assumed to be accounted for by the measured charge variations among the seven sites. Variations in the dose rates as a detector moved away from the center of the phantom were evaluated with Monte Carlo simulations by moving the detector up to 0.2 mm 12,13 . The uncertainty of this deviation was not included because the variations were within the simulation uncertainty.…”

Section: Resultsmentioning

confidence: 99%

“…Variations in the dose rates as a detector moved away from the center of the phantom were evaluated with Monte Carlo simulations by moving the detector up to 0.2 mm. 12,13 The uncertainty of this deviation was not included because the variations were within the simulation uncertainty. The thermometer and barometer calibration uncertainties were less than 0.01% and were thus ignored.…”

Section: Uncertainty Analysismentioning

confidence: 99%

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Consistency of dose rates after applying machine‐specific reference correction factors for the gamma knife 16 mm collimator field

et al. 2023

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Background The machine‐specific reference (msr) correction factors (kQmsr,Q0fmsr,fref$k_{{Q_{{\rm{msr}}}},\;{Q_0}}^{{f_{{\rm{msr}}}},{f_{{\rm{ref}}}}}$) were introduced in International Atomic Energy Agency (IAEA) Technical Report Series 483 (TRS‐483) for reference dosimetry of small fields. Several correction factor sets exist for a Leksell Gamma Knife (GK) Perfexion or Icon. Nevertheless, experiments have not rigorously validated the correction factors from different studies. Purpose This study aimed to assess the role and accuracy of kQmsr,Q0fmsr,fref$k_{{Q_{{\rm{msr}}}},\;{Q_0}}^{{f_{{\rm{msr}}}},{f_{{\rm{ref}}}}}$ values in determining the absorbed dose rates to water in the reference dosimetry of Gamma Knife. Methods The dose rates in the 16 mm collimator field of a GK were determined following the international code of practices with three ionization chambers: PTW T31010, PTW T31016 (PTW Freiberg GmbH, New York, NY), and Exradin A16 (Standard Imaging, Inc., Middleton, WI). A chamber was placed at the center of a solid water phantom (Elekta AB, Stockholm, Sweden) using a detector‐specific insert. The reference point of the ionization chamber was confirmed using cone‐beam CT images. Consistency checks were repeated five times at a GK site and performed once at seven GK sites. Correction factors from six simulations reported in previous studies were employed. Variations in the dose rates and relative dose rates before and after applying the kQmsr,Q0fmsr,fref$k_{{Q_{msr}},\;{Q_0}}^{{f_{msr}},{f_{ref}}}$ were statistically compared. Results The standard deviation of the dose rates measured by the three chambers decreased significantly after any correction method was applied (p = 0.000). When the correction factors of all studies were averaged, the standard deviation was reduced significantly more than when any single correction method was applied (p ≤ 0.030), except for the IAEA TRS‐483 correction factors (p = 0.148). Before any correction was applied, there were statistically significant differences among the relative dose rates measured by the three chambers (p = 0.000). None of the single correction methods could remove the differences among the ionization chambers (p ≤ 0.038). After TRS‐483 correction, the dose rate of Exradin A16 differed from those of the other two chambers (p ≤ 0.025). After the averaged factors were applied, there were no statistically significant differences between any pairs of chambers according to Scheffe's post hoc analyses (p ≥ 0.051); however, PTW T31010 differed from PTW 31016 according to Tukey's HSD analyses (p = 0.040). Conclusion The kQmsr,Q0fmsr,fref$k_{{Q_{{\rm{msr}}}},\;{Q_0}}^{{f_{{\rm{msr}}}},{f_{{\rm{ref}}}}}$ significantly reduced variations in the dose rates measured by the three ionization chambers. The mean correction factors of the six simulations produced the most consistent results, but this finding was not explicitly proven in the statistical analyses.

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Section: Resultsmentioning

confidence: 99%

Section: Uncertainty Analysismentioning

confidence: 99%

Consistency of dose rates after applying machine‐specific reference correction factors for the gamma knife 16 mm collimator field

et al. 2023

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“…However, no volume averaging correction factors for commonly used detectors for Gamma Knife dosimetry have been available in the literature so far. Rarely published research on this topic involved custom‐printed isodose‐shaped scintillator detectors 19 . The lack of research can be primarily contributed to the complex geometry of the Gamma Knife radiation delivery system where multiple beams are incident on the detector from numerous different directions creating an elliptical absorbed dose distribution and making the calculations of volume averaging correction factor more complex.…”

Section: Introductionmentioning

confidence: 99%

“…Rarely published research on this topic involved custom‐printed isodose‐shaped scintillator detectors. 19 The lack of research can be primarily contributed to the complex geometry of the Gamma Knife radiation delivery system where multiple beams are incident on the detector from numerous different directions creating an elliptical absorbed dose distribution and making the calculations of volume averaging correction factor more complex. Accurate determination of volume averaging correction factors in such narrow beams involves modification of current formalism from 2D to 3D approach and integration of the absorbed dose distribution over detector volume.…”

Section: Introductionmentioning

confidence: 99%

Determination of volume averaging correction factors using an elliptical absorbed dose model for Gamma Knife Perfexion

Šegedin,

Hršak,

Babić

et al. 2023

J Applied Clin Med Phys

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PurposeThe purpose of this study is to calculate volume averaging correction factors for detectors used in the dosimetry of Gamma Knife's narrow photon beams, and to determine the impact of volume averaging on the field output correction factor.MethodsSimulations of different Gamma Knife fields were done using elliptical dose model formalism with newly introduced fit functions. To determine volume averaging correction factors a calculation of the absorbed dose over the volume of the detector was performed. The elliptical dose model was tested with respect to absorbed dose distribution for different volumes and compared with the calculations of Leksell GammaPlan v.11.3.1.ResultsThe largest differences in absorbed dose calculated by the elliptical model and Leksell GammaPlan are 2.25%, 1.5%, and 0.6% for 16, 8, and 4 mm field sizes, respectively. Volume averaging correction factors were determined for six ionization chambers, five semiconductor detectors, a diamond, and two plastic scintillator detectors. In general, for all examined detectors the impact of volume averaging is more pronounced for smaller field sizes. All studied ionization chambers had a larger volume than other detectors, therefore the volume averaging correction factors for ionization chambers are larger for all investigated field sizes. Besides the fact that plastic scintillator detectors can be considered tissue‐equivalent, volume averaging correction factor should be applied.ConclusionVolume averaging correction factors for different detectors are determined and suitable detectors for dosimetry of Gamma Knife's narrow photon beams are recommended. It is shown that volume averaging has a dominant contribution to a field output correction factor.

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Verification of mean dose in a tumor using 3D-printed tumor-model scintillators in anthropomorphic phantoms and a spherical phantom

Seo,

Kim,

Choi

et al. 2024

Nuclear Engineering and Technology

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Feasibility of isodose‐shaped scintillation detectors for the measurement of gamma knife output factors

Cited by 3 publications

References 25 publications

Consistency of dose rates after applying machine‐specific reference correction factors for the gamma knife 16 mm collimator field

Consistency of dose rates after applying machine‐specific reference correction factors for the gamma knife 16 mm collimator field

Determination of volume averaging correction factors using an elliptical absorbed dose model for Gamma Knife Perfexion

Verification of mean dose in a tumor using 3D-printed tumor-model scintillators in anthropomorphic phantoms and a spherical phantom

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