Monte carlo determination of correction factors for dosimetric measurements in gamma knife perfexion small fields

Zoros, E.; Pappas, E.; Moutsatsos, A.; Pantelis, E.; Paraskevopoulou, Chryssa; Georgiou, Evangelos; Karaiskos, P.

doi:10.1016/j.ejmp.2016.07.494

Cited by 2 publications

(3 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Response of detectors in small fields and the determination of detector‐specific output correction factors have been extensively investigated for a range of detectors by several research groups, using one of the following three techniques: (a) empirical approach, where uncorrected signal ratios were determined and compared to the field output factors determined with reference detectors, (b) numerical approach, where

k_{Q_{italicclin}, Q_{italicref}}^{f_{italicclin}, f_{italicref}}

were determined with MC simulations, and (c) semi‐empirical approach which combines both, measurements and numerical/analytical calculations, and where

k_{Q_{italicclin}, Q_{italicref}}^{f_{italicclin}, f_{italicref}}

were the most commonly determined through the comparison of measured uncorrected detector's signal ratios with MC calculated field output factors . There are advantages and disadvantages of each of these approaches .…”

Section: Introductionmentioning

confidence: 99%

A novel method for the determination of field output factors and output correction factors for small static fields for six diodes and a microdiamond detector in megavoltage photon beams

et al. 2018

View full text Add to dashboard Cite

Purpose The goal of this work is to provide a large and consistent set of data for detector‐specific output correction factors, kQitalicclin,Qitalicref0.166667emfitalicclin,fref, for small static fields for seven solid‐state detectors and to determine field output factors, ΩQitalicclin,Qitalicreffclin,fref, using EBT3 radiochromic films and W1 plastic scintillator as reference detectors on two different linear accelerators and four megavoltage photon beams. Consistent measurement conditions and recommendations given in the International Code of Practice TRS‐483 for small‐field dosimetry were followed throughout the study. Methods ΩQitalicclin,Qitalicreffclin,fref were determined on two linacs, Elekta Versa HD and Varian TrueBeam, for 6 and 10 MV beams with and without flattening filter and for nine fields ranging from 0.5 × 0.5 cm2 to 10 × 10 cm2. Signal readings obtained with EBT3 radiochromic films and W1 plastic scintillator were fitted by an analytical function. Volume averaging correction factors, determined from two‐dimensional (2D) dose matrices obtained with EBT3 films and fitted to bivariate Gaussian function, were used to correct measured signals. kQitalicclin,Qitalicreffclin,fref were determined empirically for six diodes, IBA SFD, IBA Razor, PTW 60008 P, PTW 60012 E, PTW 60018 SRS, and SN EDGE, and a PTW 60019 microDiamond detector. Results Field output factors and detector‐specific kQitalicclin,Qitalicreffclin,fref are presented in the form of analytical functions as well as in the form of discrete values. It is found that in general, for a given linac, small‐field output factors need to be determined for every combination of beam energy and filtration (WFF or FFF) and field size as the differences between them can be statistically significant (P < 0.05). For different beam energies, the present data for kQitalicclin,Qitalicreffclin,fref are found to differ significantly (P < 0.05) from the corresponding data published in TRS‐483 mostly for the smallest fields (<1.5 cm). For the PTW microDiamond detector, statistically significant differences (P < 0.05) between kQitalicclin,Qitalicreffclin,fref values were found for all investigated beams on an Elekta Versa HD linac for field sizes 0.5 × 0.5 cm2 and 0.8 × 0.8 cm2. Significant differences in kQitalicclin,Qitalicreffclin,fref between beams of a given energy but with and without flattening filters are found for measurements made in small fields (<1.5 cm) at a given linac. Differences in kQitalicclin,Qitalicreffclin,fref are also found when measurements are made at different linacs using the same beam energy filtration combination; for the PTW microDiamond detector, these differences were found to be around 6% and were considered as significant. Conclusions Selection of two reference detectors, EBT3 films and W1 plastic scintillator, and use of an analytical function, is a novel approach for the determination of ΩQitalicclin,Qitalicreffclin,fref for small static fields in megavoltage photon beams. Large set of kQitalicclin,Qitalicreffclin,fref data for s...

show abstract

k_{Q_{italicclin}, Q_{italicref}}^{f_{italicclin}, f_{italicref}}

were determined with MC simulations, and (c) semi‐empirical approach which combines both, measurements and numerical/analytical calculations, and where

k_{Q_{italicclin}, Q_{italicref}}^{f_{italicclin}, f_{italicref}}

Section: Introductionmentioning

confidence: 99%

A novel method for the determination of field output factors and output correction factors for small static fields for six diodes and a microdiamond detector in megavoltage photon beams

et al. 2018

View full text Add to dashboard Cite

show abstract

“…For small field dosimetry, it is crucial to determine the field output correction factor

k_{{Q}_{msr},\ {Q}_{clin}\ }^{{f}_{msr},\ {f}_{clin}}

to be able to correct the detector's reading and account for the abovementioned nonequilibrium conditions in machine‐specific reference f msr (msr) and clinical fields f clin (clin) with beam qualities Q msr and Q clin . Together with the field output factor (OF)

{{\Omega}}_{{Q}_{msr},\ {Q}_{clin}}^{{f}_{msr},{f}_{clin}}

determination, these were the focus of investigation performed by different groups 2–11 . OF and field output correction factor determination for different detectors can be performed by measurements or with Monte Carlo (MC) simulations.…”

Section: Introductionmentioning

confidence: 99%

“…Together with the field output factor (OF)

determination, these were the focus of investigation performed by different groups. 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 OF and field output correction factor determination for different detectors can be performed by measurements or with Monte Carlo (MC) simulations. In general, field output correction factors are a product of four different perturbations in the small field; ratios of water‐to‐detector‐medium stopping powers in the clinical and machine‐specific reference field, volume averaging, fluence, and of spectral perturbations in clinical and machine‐specific reference fields.…”

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

View full text Add to dashboard Cite

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.

show abstract

Monte carlo determination of correction factors for dosimetric measurements in gamma knife perfexion small fields

Cited by 2 publications

References 0 publications

A novel method for the determination of field output factors and output correction factors for small static fields for six diodes and a microdiamond detector in megavoltage photon beams

A novel method for the determination of field output factors and output correction factors for small static fields for six diodes and a microdiamond detector in megavoltage photon beams

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

Contact Info

Product

Resources

About