Flattening filter free beams from TrueBeam and Versa HD units: Evaluation of the parameters for quality assurance

Fogliata, Antonella; Fleckenstein, Jens; Schneider, Frank E.; Pachoud, M.; Ghandour, S.; Krauss, H.; Reggiori, G.; Stravato, A.; Lohr, Frank; Scorsetti, Marta; Cozzi, Luca

doi:10.1118/1.4938060

Cited by 28 publications

(31 citation statements)

References 13 publications

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“…The surface doses measured in this study for one open field were 45%, 44%, 39% and 33% of the dose maximum for flattened and unflattened 6 and 10 MV energies, respectively. The results are in line with previously performed studies [21,22]. However, the surface doses are more complex for modulated beams as the dose is accumulated from primary beam, treatment head scatter, MLC transmission, scattered and contaminating electrons, and further on these all dependent on energy, field size, source-to-skin distance, patient geometry and direction of the beam.…”

Section: Discussionsupporting

confidence: 91%

Surface doses of flattening filter free beams with volumetric modulated arc therapy dose delivery for breast cancer

Seppälä

Voutilainen

Heikkilä

et al. 2017

Physics and Imaging in Radiation Oncology

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Background and purpose: Flattening filter free (FFF) beams enable high-dose rate irradiations and have the potential to speed up breast cancer radiotherapy (RT) treatments. In this work the surface doses of FFF beams were studied with various treatment plans for breast cancer RT. The near surface dose distributions were compared to the ones delivered with conventional flattening filter (FF) beams and to the calculated dose distributions. Materials and methods: The study was executed with radiochromic films. In addition to one open field, four techniques were investigated: tangential open field, tangential IMRT (IMRT), tangential VMAT (tVMAT) and continuous VMAT (cVMAT) techniques, respectively. The dose distributions were calculated with commercial Monte Carlo (MC) algorithm with energies of 6 and 10 MV with both FF and FFF. The surface areas investigated were divided into depths of 0-2, 2-5 and 5-8 mm. Results: The largest deviations (on average 5.9%) between the measured and calculated doses were recorded at the most shallowest depths (0-2 mm). At deeper depths, the differences were on average 1.4% and always less than 6%. The measured near surface doses were slightly lower (4.6%) with modulated 6MVFFF beams than with the corresponding flattened beams and on the contrary with 10 MV the surface doses by FFF were slightly higher (2.8%). Conclusions: The studied MC calculation algorithm was accurate in determine the near surface doses. There was no significant difference in measured or calculated surface doses between FFF and FF beams. With respect to surface dose uniformity the VMAT techniques overall resulted in the most uniform dose distributions.

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Section: Discussionsupporting

confidence: 91%

Surface doses of flattening filter free beams with volumetric modulated arc therapy dose delivery for breast cancer

Seppälä

Voutilainen

Heikkilä

et al. 2017

Physics and Imaging in Radiation Oncology

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“…For FFF beams, renormalization was needed to identify the penumbra regions. The renormalization factors provided by Fogliata et al . were used to normalize the profile of the FFF beams.…”

Section: Methodsmentioning

confidence: 99%

Do the representative beam data for TrueBeam^™ linear accelerators represent average data?

Tanaka

Mizuno

Akino

et al. 2019

J Applied Clin Med Phys

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If the vendor's representative beam data (RBD) for TrueBeam linear accelerators are to be valid for use in clinical practice, the variations in the beam data used for beam modeling must be small. Although a few studies have reported the variation of the beam data of the TrueBeam machines, the numbers of machines analyzed in those studies were small. In this study, we investigated the variation in the beam data for 21 TrueBeam machines collected from 17 institutions with their agreement. In the exponential regions, the percent depth dose (PDD) values showed very small variation, <1% for all the photon energies analyzed. Similarly, the off‐center ratio (OCR) values also showed small variation for all energies. In the field regions, the standard deviations of the values of dose difference (DD) between the data for each machine and the study average were <1% for field sizes ≥100 × 100 mm2. The maximum distance‐to‐agreement from the average data was <0.5 mm in the penumbra regions. The output factor (OPF) values also showed very small variation (<1%) for all energies and field sizes. Both the PDD and OCR of the average study data showed good agreement with the vendor's RBD for field sizes ≥100 × 100 mm2. The OPF of the average study data also showed good agreement with the vendor's RBD for all field sizes. However, although all the institutions used ionization chambers with similar cavity volumes, the 30 × 30 mm2 field size showed large DD variations (≥2%) in OCR in the field regions. We conclude that the intermachine variability of TrueBeam linear accelerators was very small except for small field dosimetry, supporting the validity of the use of the RBD for clinical applications. The use of the vendor's RBD might greatly facilitate the quick installation of a new linear accelerator.

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“…Table 24 in TRS 483 1 reports those correction factors for different detectors and a range S clin from 0.4 to 8 cm for tomotherapy machines. The PTW-31016 PinPoint 3D, the 60018 unshielded diode, and the 60019 microDiamond appear in the referred table.…”

Section: B Relative Dosimetryoutput Factors In Htmentioning

confidence: 99%

“…1 Again following the recommendations concerning small fields, 1 the field sizes at the measurement depth have been estimated through the measured profiles FWHM, for Y. For X, as the 50% of maximum dose may be located within the in-field region of the FFF profile, the measured width may not correspond to the correct field size and in HT the normalization methods proposed for FFF beams for conventional linear accelerators 23,24 cannot be used. The field size for X was thus obtained multiplying the nominal width by the scale factor of 95/85 accounting for the setup.…”

Section: B Relative Dosimetryoutput Factors In Htmentioning

confidence: 99%

Application of the TRS 483 code of practice for reference and relative dosimetry in tomotherapy

et al. 2019

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Purpose To apply the recent code of practice from the IAEA/AAPM, TRS 483, to helical tomotherapy (HT) for reference and relative dosimetry obtaining correction factors for the Exradin A1SL ionization chamber. Methods The beam quality correction factor for the A1SL chamber was obtained through three different approaches following TRS 483 concepts and compared with published values. The determination of the reference absolute dose for the machine‐specific reference (msr) field was complemented with relative dosimetry through the determination of output factors of small fields using different detectors. The response of A1SL was compared with correction‐free film results and corrected output factors of other detectors. Results A weighted mean beam quality correction factor of 0.9945± 0.0073 was obtained for the A1SL chamber which is in agreement with values reported in the literature. Output factors obtained with different detectors were in agreement, given the uncertainty level. Considering the film output factors as free of corrections, the average value for A1SL output factors corrections was 1.000 ± 0.007. Conclusions The beam quality correction factors for the A1SL chamber obtained through the three different pathways recommended by TRS 483 agreed with each other and also with published values. The measurements from the A1SL chamber normalized to the msr field in HT can be taken as output factors for small clinical field sizes without further corrections.

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Flattening filter free beams from TrueBeam and Versa HD units: Evaluation of the parameters for quality assurance

Abstract: Renormalization factor and unflatness parameters evaluated from Varian and Elekta FFF beams are provided, in particular renormalization factors table and fit parameters.

Cited by 28 publications

References 13 publications

Surface doses of flattening filter free beams with volumetric modulated arc therapy dose delivery for breast cancer

Surface doses of flattening filter free beams with volumetric modulated arc therapy dose delivery for breast cancer

Do the representative beam data for TrueBeam^™ linear accelerators represent average data?

Application of the TRS 483 code of practice for reference and relative dosimetry in tomotherapy

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Flattening filter free beams from TrueBeam and Versa HD units: Evaluation of the parameters for quality assurance

Abstract: Renormalization factor and unflatness parameters evaluated from Varian and Elekta FFF beams are provided, in particular renormalization factors table and fit parameters.

Cited by 28 publications

References 13 publications

Surface doses of flattening filter free beams with volumetric modulated arc therapy dose delivery for breast cancer

Surface doses of flattening filter free beams with volumetric modulated arc therapy dose delivery for breast cancer

Do the representative beam data for TrueBeam™ linear accelerators represent average data?

Application of the TRS 483 code of practice for reference and relative dosimetry in tomotherapy

Contact Info

Product

Resources

About

Do the representative beam data for TrueBeam^™ linear accelerators represent average data?