Prospective Monte Carlo Simulation for Choosing High Efficient Detectors for Small-Field Dosimetry

Donya, Hossam; Seniwal, Baljeet; Darwesh, Reem; Fonseca, Telma Cristina Ferreira

doi:10.5772/intechopen.89150

Cited by 4 publications

(2 citation statements)

References 117 publications

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“…The size of the source is generally less than 5 mm, and hence the loss of LCPE would occur for radiation beams with a radius less than 5 mm. 8 Other literature suggests there is dependence on focal spot size in small field dosimetry; however, such an effect can only be seen for extremely small fields (<5 × 5 mm 2 ). 5,9 Moigner et al, Liu et al and Czarnecki et al have shown that there is not much dependence on source sizes of different machines for small fields.…”

Section: Introductionmentioning

confidence: 97%

Evaluation of dosimetric parameters of small fields of 6 MV flattening filter free photon beam measured using various detectors against Monte Carlo simulation

et al. 2020

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Purpose: This study aims to evaluate dosimetric parameters like percentage depth dose, dosimetric field size, depth of maximum dose surface dose, penumbra and output factors measured using IBA CC01 pinpoint chamber, IBA stereotactic field diode (SFD), PTW microDiamond against Monte Carlo (MC) simulation for 6 MV flattening filter-free small fields. Materials and Methods: The linear accelerator used in the study was a Varian TrueBeam® STx. All field sizes were defined by jaws. The required shift to effective point of measurement was given for CC01, SFD and microdiamond for depth dose measurements. The output factor of a given field size was taken as the ratio of meter readings normalised to 10 × 10 cm2 reference field size without applying any correction to account for changes in detector response. MC simulation was performed using PRIMO (PENELOPE-based program). The phase space files for MC simulation were adopted from the MyVarian Website. Results and Discussion: Variations were seen between the detectors and MC, especially for fields smaller than 2 × 2 cm2 where the lateral charge particle equilibrium was not satisfied. Diamond detector was seen as most suitable for all measurements above 1 × 1 cm2. SFD was seen very close to MC results except for under-response in output factor measurements. CC01 was observed to be suitable for field sizes above 2 × 2 cm2. Volume averaging effect for penumbra measurements in CC01 was observed. No detector was found suitable for surface dose measurement as surface ionisation was different from surface dose due to the effect of perturbation of fluence. Some discrepancies in measurements and MC values were observed which may suggest effects of source occlusion, shift in focal point or mismatch between real accelerator geometry and simulation geometry. Conclusion: For output factor measurement, TRS483 suggested correction factor needs to be applied to account for the difference in detector response. CC01 can be used for field sizes above 2 × 2 cm2 and microdiamond detector is suitable for above 1 × 1 cm2. Below these field sizes, perturbation corrections and volume averaging corrections need to be applied.

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Section: Introductionmentioning

confidence: 97%

Evaluation of dosimetric parameters of small fields of 6 MV flattening filter free photon beam measured using various detectors against Monte Carlo simulation

et al. 2020

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“…However, small field beams have several unique physical properties that necessitate special care in measuring their absorbed doses to water 1 . The volume averaging effect, the lack of lateral charged particle equilibrium, and different detector responses due to beam quality differences are typical characteristics of small fields that necessitate meticulous handling 2–6 . The International Atomic Energy Agency and the American Association of Physicists in Medicine published TRS‐483, a code of practice for the reference and relative dosimetry of small fields, in 2017 2 .…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2022

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Purpose Scintillation detectors were 3D printed based on a gamma knife (GK) dose distribution to calculate the volume averaging effect. The collimator output factors were measured using isodose‐shaped scintillators (ISSs) and compared with those of a micro‐diamond detector and previous reports. Methods An absorbed dose distribution in a spherical dosimetry phantom with a radius of 8 cm was obtained from GK treatment planning software (Leksell GammaPlan [LGP], Elekta AB, Stockholm, Sweden). Two types of ISSs were fabricated to fit the 97.2% (ISS‐1) and 95.6% (ISS‐2) isodose surfaces. The volume averaging correction factors were obtained by dividing the absorbed dose to water in the central voxel (CV) by that in the ISS. The correction effect due to the difference between the ISS and water was calculated by Monte Carlo simulations. Ten ISS detectors, five of each type, were used to measure the output factors of the 4‐ and 8‐mm collimators of a GK Icon to assess system consistency. The output factors of seven GKs were measured using two ISS detectors, one of each type, and a PTW T60019 (PTW, Freiburg, Germany) micro‐diamond detector. Results The detector output ratios (DORs) measured using the five ISSs of each type were consistent, with standard uncertainties less than 0.2%. In the 4‐mm field, the volume averaging correction factor ratios were 1.018 and 1.026, and the output factors after all corrections were 0.827 (0.006) and 0.825 (0.006) for ISS‐1 and ISS‐2, respectively. In the 8‐mm field, the volume averaging correction factor ratios were 1.000 for both ISS types, and the output factors were 0.898 (0.003) and 0.900 (0.003) for ISS‐1 and ISS‐2, respectively. The ISS detectors could measure the output factors of a GK with uncertainties comparable to that of the PTW 60019 detector. The output factors of all detectors decreased with the dose rate. Conclusion The volume averaging effect of an ISS developed in‐house could be calculated using known dose distributions. The collimator output factors of the GK Perfexion/Icon models measured using ISS detectors were consistent with those of a commercial synthetic micro‐diamond detector and recent studies.

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Accuracy of Acuros$$^{\text {TM}}$$ BV as determined from GATE monte-carlo simulation

2022

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The American Association of Physicists in Medicine’s Task Group No.43 has provided a standardised dose calculation methodology that is now the international benchmark for all brachytherapy dosimetry publications and treatment planning systems. However, limitations in this methodology has seen the development of Model-Based Dose Calculation Algorithms (MBDCA). In 2009, Varian (Varian Medical Systems, Palo Alto, CA, USA) released Acuros$$^{\text {TM}}$$ TM BrachyVision (ABV) which calculates dose by explicitly solving the Linear Boltzmann Transport Equation. In this study we have assessed the accuracy of ABV dose calculations within a range of materials relevant to high dose rate brachytherapy with an iridium-192 ($$^{\text {192}}$$ 192 Ir) source. Accuracy assessment has been achieved by implementing a modelled GamaMed Plus $$^{\text {192}}$$ 192 Ir source within a series of phantoms using the GEANT4 Application for Emission Tomography (GATE) to calculate dose for comparison with dose as determined by ABV. Comparisons between GATE and ABV were made using point-to-point profile comparisons and 1D gamma analysis. Source validation results yielded good agreement with published data. Spectrum and TG43U1 comparisons showed no major differences, with TG43U1 comparisons agreeing within ± 1%. Point-to-point comparisons showed large differences between GATE and ABV near the source and in low density materials. 1D gamma analysis pass criteria of 2%/1 mm and 2%/2 mm yielded passing rates ranging between 51.72–100% and 62.07–100% respectively. A critical analysis of this study’s results suggest that ABV is unable to accurately calculate doses in low density materials. Furthermore, spatial accuracy of dose near the source is within 2 mm.

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Prospective Monte Carlo Simulation for Choosing High Efficient Detectors for Small-Field Dosimetry

Cited by 4 publications

References 117 publications

Evaluation of dosimetric parameters of small fields of 6 MV flattening filter free photon beam measured using various detectors against Monte Carlo simulation

Evaluation of dosimetric parameters of small fields of 6 MV flattening filter free photon beam measured using various detectors against Monte Carlo simulation

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

Accuracy of Acuros$$^{\text {TM}}$$ BV as determined from GATE monte-carlo simulation

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