The influence of small field output factors simulated uncertainties on the calculated dose in VMAT plans for brain metastases: a multicentre study

Clemente, Stefania; Falco, M.D.; Cagni, E.; Talamonti, Cinzia; Boccia, Mafalda; Gino, Eva; Lorenzini, Elena; Rosica, F.; Russo, S.; Alparone, A.; Zefiro, Daniele; Fiandra, C.

doi:10.1259/bjr.20201354

Cited by 2 publications

(4 citation statements)

References 32 publications

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“…The brainstem max dose was 1.6±0.9% lower for the corrected plans with a p value of 0.03, for 6 WFF, and 1.8±1.5% lower for the corrected plans, with a p value of 0.1, for 6 FFF. Clemente et al has also investigated the impact of small field output factor inaccuracies on VMAT SRS brain plans [31]. However, their methodology differed slightly, in that they simulated output factor errors by changing the values positively and negatively with well-defined amounts.…”

Section: Discussionmentioning

confidence: 99%

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Effect of inaccurate small field output factors on brain SRS plans

Dobberthien¹,

Cao²,

Zhao³

et al. 2022

Biomed. Phys. Eng. Express

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External beam radiotherapy often includes the use of field sizes 3 × 3 cm2 or less, which can be defined as small fields. Dosimetry is a difficult, yet important part of the radiotherapy process. The dosimetry of small fields has additional challenges, which can lead to treatment inconsistencies if not done properly. Most important is the use of an appropriate detector, as well as the application of the necessary corrections. The International Atomic Energy Agency and the American Association of Physicists in Medicine provide the International Code of Practice (CoP) TRS-483 for the dosimetry of small static fields used in external MV photon beams. It gives guidelines on how to apply small-field correction factors for small field dosimetry. The purpose of this study was to evaluate the impact of inaccurate small-field output factors on clinical brain stereotactic radiosurgery plans with and without applying the small-field correction factors as suggested in the CoP. Small-field correction factors for a Varian TrueBeam linear accelerator were applied to uncorrected relative dose factors. Uncorrected and corrected clinical plans were created with two different beam configurations, 6 MV with a flattening filter (6 WFF) and 6 MV without a flattening filter (6 FFF). For the corrected plans, the planning target volume mean dose was 1.6 ± 0.9% lower with p < 0.001 for 6 WFF and 1.8 ± 1.5% lower with p < 0.001 for 6 FFF. For brainstem, a major organ at risk, the corrected plans had a dose that was 1.6 ± 0.9% lower with p = 0.03 for 6 WFF and 1.8 ± 1.5% lower with p = 0.10 for 6 FFF. This represents a systematic error that should and can be corrected.

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Section: Discussionmentioning

confidence: 99%

“…Apart from the simulation of brain SRS plans, Clemente et al also compared the influence from jawdefined and MLC-defined fields [31]. For the purpose of applying correction factors to output factors, we chose to define the field by the FWHM of the field as measured, so that we could use the factors from the reference directly [32].…”

Section: Introductionmentioning

confidence: 99%

Effect of inaccurate small field output factors on brain SRS plans

Dobberthien¹,

Cao²,

Zhao³

et al. 2022

Biomed. Phys. Eng. Express

View full text Add to dashboard Cite

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“…Only the consequences for the dose calculation of intensity modulated radiotherapy (IMRT) plans when using a Farmer chamber for dose profile measurements were investigated. 15 The consequences of using incorrect small field output factors were quantified for IMRT, 16 volumetric modulated arc therapy (VMAT), 17 and small 3D-planned cranial lesions. 18 Once a model is completed, verification is limited by the available measurement devices and their geometries as well as the quality metrics and tolerance criteria used.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Simulation of consequences of using nonideal detectors during beam data commissioning measurements

Wegener,

Sauer

2023

Medical Physics

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BackgroundBeam data commissioning is a core task of radiotherapy physicists. Despite multiple detectors available, a feasible measurement program compromises between detector properties and time constraints. Therefore, it is important to understand how nonideal measurement data propagates into patient dose calculation.PurposeWe simulated the effects of realistic errors, due to beam commissioning with presumably nonoptimal detectors, on the resulting patient dose distributions. Additionally, the detectability of such beam commissioning errors during patient plan quality assurance (QA) was evaluated.MethodsA clinically used beam model was re‐commissioned introducing changes to depth dose curves, output factors, profiles or combinations of those. Seventeen altered beam models with incremental changes of the modelling parameters were created to analyze dose changes on simplified anatomical phantoms. Additionally, fourteen altered models incorporate changes in the order of signal differences reported for typically used detectors. Eighteen treatment plans of different types were recalculated on patient CT data sets using the altered beam models.ResultsFor the majority of clinical plans, dose distributions in the target volume recalculated on the patient computed tomography data were similar between the original and the modified beam models, yielding global 2%/2 mm gamma pass rates above 98.9%. Larger changes were observed for certain combinations of beam modelling errors and anatomical sites, most extreme for output factor changes in a small target volume plan with a pass rate of 80.6%. Modelling an enlarged penumbra as if measured with a 0.125 cm3 ion chamber had the largest effect on the dose distribution (average pass rate of 96.5%, lowest 85.4%). On different QA phantom geometries, dose distributions between calculations with modified and unmodified models typically changed too little to be detected in actual measurements.ConclusionWhile the simulated errors during beam modelling had little effect on most plans, in some cases changes were considerable. High‐quality penumbra and small field output factor should be a main focus of commissioning measurements. Detecting modelling issues using standard patient QA phantoms is unlikely. Verification of a beam model should be performed especially for plans with high modulation and in different depths or geometries representing the variety of situations expected clinically.

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The influence of small field output factors simulated uncertainties on the calculated dose in VMAT plans for brain metastases: a multicentre study

Cited by 2 publications

References 32 publications

Effect of inaccurate small field output factors on brain SRS plans

Effect of inaccurate small field output factors on brain SRS plans

Simulation of consequences of using nonideal detectors during beam data commissioning measurements

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