Beam properties and stability of a flattening‐filter free 7 MV beam—An overview

Dzierma, Yvonne; Licht, Norbert; Nuesken, Frank; Ruebe, Christian

doi:10.1118/1.3703835

Cited by 35 publications

(33 citation statements)

References 29 publications

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“…As shown in Figure 4b and c, the off-axis profiles have convex distributions that agree with the literature. [310131516181920] The profile in the off-axis direction at the 0.7-cm depth, where many contamination electrons are contained, differs from the profiles at deeper positions under the influence of entrained electrons. This is because the electron beam spreads laterally after entering water and is larger than X-rays, as shown in Figure 4a.…”

Section: Resultsmentioning

confidence: 99%

“…The dose distribution for FFF linacs determined using Monte Carlo (MC) simulations,[34567891011] as well as measured data from treatment apparatuses in clinical use,[89101112131415161718] has been published. Most of such experimental studies employed commercial linacs with a metal plate, such as copper or aluminum, inserted to absorb the primary and secondary electrons created in materials in the linac head.…”

Section: Introductionmentioning

confidence: 99%

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Beam characterization of 10-MV photon beam from medical linear accelerator without flattening filter

et al. 2017

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Aim:This work investigated the dosimetric properties of a 10-MV photon beam emitted from a medical linear accelerator (linac) with no flattening filter (FF). The aim of this study is to analyze the radiation fluence and energy emitted from the flattening filter free (FFF) linac using Monte Carlo (MC) simulations.Materials and Methods:The FFF linac was created by removing the FF from a linac in clinical use. Measurements of the depth dose (DD) and the off-axis profile were performed using a three-dimensional water phantom with an ionization chamber. A MC simulation for a 10-MV photon beam from this FFF linac was performed using the BEAMnrc code.Results:The off-axis profiles for the FFF linac exhibited a chevron-like distribution, and the dose outside the irradiation field was found to be lower for the FFF linac than for a linac with an FF (FF linac). The DD curves for the FFF linac included many contaminant electrons in the build-up region.Conclusion:Therefore, for clinical use, a metal filter is additionally required to reduce the effects of the electron contamination. The mean energy of the FFF linac was found to be lower than that of the FF linac owing to the absence of beam hardening caused by the FF.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Beam characterization of 10-MV photon beam from medical linear accelerator without flattening filter

et al. 2017

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“…In principle, validation of the treatment planning system is already proven by the fact that dosimetric verification for IMRT plans was checked in the commissioning phase [9] and in routine quality assurance, and since the deviation of the mARC plans from the step-and-shoot plans is negligible. However, we demonstrate these measurements for completeness.…”

Section: Resultsmentioning

confidence: 99%

A novel implementation of mARC treatment for non-dedicated planning systems using converted IMRT plans

et al. 2013

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BackgroundThe modulated arc (mARC) technique has recently been introduced by Siemens as an analogue to VMAT treatment. However, up to now only one certified treatment planning system supports mARC planning. We therefore present a conversion algorithm capable of converting IMRT plans created by any treatment planning system into mARC plans, with the hope of expanding the availability of mARC to a larger range of clinical users and researchers. As additional advantages, our implementation offers improved functionality for planning hybrid arcs and provides an equivalent step-and-shoot plan for each mARC plan, which can be used as a back-up concept in institutions where only one linac is equipped with mARC.MethodsWe present a feasibility study to outline a practical implementation of mARC plan conversion using Philips Pinnacle and Prowess Panther. We present examples for three different kinds of prostate and head-and-neck plans, for 6 MV and flattening-filter-free (FFF) 7 MV photon energies, which are dosimetrically verified.ResultsIt is generally more difficult to create good quality IMRT plans in Pinnacle using a large number of beams and few segments. We present different ways of optimization as examples. By careful choosing the beam and segment arrangement and inversion objectives, we achieve plan qualities similar to our usual IMRT plans. The conversion of the plans to mARC format yields functional plans, which can be irradiated without incidences. Absolute dosimetric verification of both the step-and-shoot and mARC plans by point dose measurements showed deviations below 5% local dose, mARC plans deviated from step-and-shoot plans by no more than 1%. The agreement between GafChromic film measurements of planar dose before and after mARC conversion is excellent. The comparison of the 3D dose distribution measured by PTW Octavius 729 2D-Array with the step-and-shoot plans and with the TPS is well above the pass criteria of 90% of the points falling within 5% local dose and 3 mm distance to agreement. For all plans, the treatment time was noticeably reduced by conversion to mARC.ConclusionsWe present the feasibility test for converting IMRT step-and-shoot plans from the RTP-output of any treatment planning system (Philips Pinnacle and Prowess Panther, in our case) into mARC plans. The feasibility and dosimetric equivalence is demonstrated for the examples of a prostate and a head-and-neck patient.

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“…Linacs with FFF beams have since been released by vendors and implemented clinically at many institutions. Properties of the FFF beams for these machines, usually determined during the commissioning process, have been subsequently reported 4 , 5 , 6 . Comparisons between Monte Carlo calculations and experimental measurements have been performed to confirm that simulations accurately model accelerator geometry 7 , 8 , 9 …”

Section: Introductionmentioning

confidence: 94%

Clinically relevant investigation of flattening filter‐free skin dose

Guy

Karki

Sharma

et al. 2016

J Applied Clin Med Phys

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As flattening filter‐free (FFF) photon beams become readily available for treatment delivery in techniques such as SBRT, thorough investigation of skin dose from FFF photon beams is necessary under clinically relevant conditions. Using a parallel‐plate PTW Markus chamber placed in a custom water‐equivalent phantom, surface‐dose measurements were taken at 2×2,3×3,4×4,6×6,8×8,10×10,20×20, and 30×30 cm2 field sizes, at 80, 90, and 100 cm source‐to‐surface distances (SSDs), and with fields defined by jaws and multileaf collimator (MLC) using multiple beam energies (6X, 6XFFF, 10X, and 10XFFF). The same set of measurements was repeated with the chamber at a reference depth of 10 cm. Each surface measurement was normalized by its corresponding reference depth measurement for analysis. The FFF surface doses at 100 cm SSD were higher than flattened surface doses by 45% at 2×2 cm2 to 13% at 20×20 cm2 for 6 MV energy. These surface dose differences varied to a greater degree as energy increased, ranging from +63% at 2×2 cm2 to −2% at 20×20 cm2 for 10 MV. At small field sizes, higher energy increased FFF surface dose relative to flattened surface dose; while at larger field sizes, relative FFF surface dose was higher for lower energies. At both energies investigated, decreasing SSD caused a decrease in the ratios of FFF‐to‐flattened surface dose. Variability with SSD of FFF‐to‐flattened surface dose differences increased with field size and ranged from 0% to 6%. The field size at which FFF and flattened beams gave the same skin dose increased with decreasing beam energy. Surface dose was higher with MLC fields compared to jaw fields under most conditions, with the difference reaching its maximum at a field size between 4×4 cm2 and 6×6 cm2 for a given energy and SSD. This study conveyed the magnitude of surface dose in a clinically meaningful manner by reporting results normalized to 10 cm depth dose instead of depth of dose maximum.PACS number(s): 87.53.Bn, 87.53.Ly, 87.55.‐x, 87.55.N‐, 87.56.N‐

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Beam properties and stability of a flattening‐filter free 7 MV beam—An overview

Abstract: The 7XU beam has been commissioned for clinical use after successful modeling, stability checks, and dosimetric verification.

Cited by 35 publications

References 29 publications

Beam characterization of 10-MV photon beam from medical linear accelerator without flattening filter

Beam characterization of 10-MV photon beam from medical linear accelerator without flattening filter

A novel implementation of mARC treatment for non-dedicated planning systems using converted IMRT plans

Clinically relevant investigation of flattening filter‐free skin dose

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