Small field detector correction factors: effects of the flattening filter for Elekta and Varian linear accelerators

Tyler, Madelaine; Liu, Paul Z Y; Lee, Christopher; McKenzie, David R.; Suchowerska, Natalka

doi:10.1120/jacmp.v17i3.6059

Cited by 24 publications

(15 citation statements)

References 44 publications

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“…This is exacerbated by the removal of the flattening filter from the LINAC, which results in most of the low-energy photons to pass through and a consequent lower average beam energy 6 . As previously reported, though, deviations in small fields correction factors for silicon diodes between flattened and FFF beams are sufficiently small (up to a maximum of ± 1.7%) to allow for their potential interchangeability on the same LINAC 27 . Consistently with this result, we used the same air gap to render the Octa a 'correction-free' dosimeter for OFs measurements for all beam qualities investigated.…”

Section: Output Factorssupporting

confidence: 58%

A novel high-resolution 2D silicon array detector for small field dosimetry with FFF photon beams

et al. 2018

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Results were consistent with those for monolithic silicon array detectors designed by the CMRP and previously characterized under flattened beams only, supporting the robustness of this technology for relative dosimetry for a wide range of beam qualities and dose per pulses. In contrast to its predecessors, the design of the Octa offers an exhaustive high-resolution 2D dose map characterization, making it a unique real-time radiation detector for small field dosimetry for field sizes up to 3 cm side.

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Section: Output Factorssupporting

confidence: 58%

A novel high-resolution 2D silicon array detector for small field dosimetry with FFF photon beams

et al. 2018

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“…1 The IAEA TRS-483 CoP for small field dosimetry recommends detectors used for QA should be: small relative to the minimum field size and the range of the secondary charged particles, have a high signal to noise ratio (SNR), high spatial resolution and also be energy, dose rate, and angular independent in response. Volume averaging effects can be avoided by the use of detectors with submillimeter spatial resolution, such as the PTW microDiamond, [2][3][4][5] IBA razor diode detector, 6 and the edgeless silicon diode, 7 however, these detectors do not address some of the more serious perturbation effects. A tissue equivalent, small volume detector can be made for plastic scintillators but these detectors suffer from a large temperature and humidity dependence as well as nonlinearity at low doses.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the PTW microDiamond in edge‐on orientation for dosimetry in small fields

Brace

Alhujaili

Paino

et al. 2020

J Applied Clin Med Phys

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Purpose: The PTW microDiamond has an enhanced spatial resolution when operated in an edge-on orientation but is not typically utilized in this orientation due to the specifications of the IAEA TRS-483 code of practice for small field dosimetry. In this work the suitability of an edge-on orientation and advantages over the recommended face-on orientation will be presented. Methods: The PTW microDiamond in both orientations was compared on a Varian TrueBeam linac for: machine output factor (OF), percentage depth dose (PDD), and beam profile measurements from 10 × 10 cm 2 to a 0.5 × 0.5 cm 2 field size for 6X and 6FFF beam energies in a water tank. A quantification of the stem effect was performed in edge-on orientation along with tissue to phantom ratio (TPR) measurements. An extensive angular dependence study for the two orientations was also undertaken within two custom PMMA plastic cylindrical phantoms. Results: The OF of the PTW microDiamond in both orientations agrees within 1% down to the 2 × 2 cm 2 field size. The edge-on orientation overresponds in the build-up region but provides improved penumbra and has a maximum observed stem effect of 1%. In the edge-on orientation there is an angular independent response with a maximum of 2% variation down to a 2 × 2 cm 2 field. The PTW microDiamond in edge-on orientation for TPR measurements agreed to the CC01 ionization chamber within 1% for all field sizes. Conclusions: The microDiamond was shown to be suitable for small field dosimetry when operated in edge-on orientation. When edge-on, a significantly reduced angular dependence is observed with no significant stem effect, making it a more versatile QA instrument for rotational delivery techniques.

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“…This near water equivalent detector has a minimal sensitive volume of 0.0004 cc and is a good candidate for small-field dosimetry. Study has shown that this detector has minimal energy, temperature, and directional dependency; thus changes within these factors will not influence the measured signal [14].…”

Section: Introductionmentioning

confidence: 99%

The effect of SSD, Field size, Energy and Detector type for Relative Output Factor measurement in small photon beams as compared with Monte Carlo simulation

Setilo

Oderinde

Plessis

2019

Polish Journal of Medical Physics and Engineering

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Introduction: Small fields photon dosimetry is associated with many problems. Using the right detector for measurement plays a fundamental role. This study investigated the measurement of relative output for small photon fields with different detectors. It was investigated for three-photon beam energies at SSDs of 90, 95, 100 and 110 cm. As a benchmark, the Monte Carlo simulation was done to calculate the relative output of these small photon beams for the dose in water. Materials and Methods: 6, 10 and 15 MV beams were delivered from a Synergy LINAC equipped with an Agility 160 multileaf collimator (MLC). A CC01 ion chamber, EFD-3G diode, PTW60019 microdiamond, EBT2 radiochromic film, and EDR2 radiographic film were used to measure the relative output of the linac. Measurements were taken in water for the CC01 ion chamber, EFD-3G diode, and the PTW60019. Films were measured in water equivalent RW3 phantom slabs. Measurements were made for 1 × 1, 2 × 2, 3 × 3, 4 × 4, 5 × 5 and a reference field of 10 × 10 cm2. Field sizes were defined at 100cm SSD. Relative output factors were also compared with Monte Carlo (MC) simulation of the LINAC and a water phantom model. The influence of voxel size was also investigated for relative output measurement. Results and Discussion: The relative output factor (ROF) increased with energy for all fields large enough to have lateral electronic equilibrium (LEE). This relation broke down as the field sizes decreased due to the onset of lateral electronic disequilibrium (LED). The high-density detector, PTW60019 gave the highest ROF for the different energies, with the less dense CC01 giving the lowest ROFs. Conclusion: These are results compared to MC simulation, higher density detectors give higher ROF values. Relative to water, the ROF measured with the air-chamber remained virtually unchanged. The ROFs, as measured in this study showed little variation due to increased SSDs. The effect of voxel size for the Monte Carlo calculations in water does not lead to significant ROF variation over the small fields studied.

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Small field detector correction factors: effects of the flattening filter for Elekta and Varian linear accelerators

Cited by 24 publications

References 44 publications

A novel high-resolution 2D silicon array detector for small field dosimetry with FFF photon beams

A novel high-resolution 2D silicon array detector for small field dosimetry with FFF photon beams

Evaluation of the PTW microDiamond in edge‐on orientation for dosimetry in small fields

The effect of SSD, Field size, Energy and Detector type for Relative Output Factor measurement in small photon beams as compared with Monte Carlo simulation

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