Independent quality assurance of a helical tomotherapy machine using the dose magnifying glass

Wong, Jeannie Hsiu Ding; Hardcastle, Nicholas; Bayliss, Adam; Tolakanahalli, Ranjini; Lerch, Michael L. F; Petasecca, Marco; Carolan, Martin G; Metcalfe, Peter E; Rosenfeld, Anatoly B.

doi:10.1118/1.3566067

Cited by 10 publications

(10 citation statements)

References 12 publications

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“…The diode detector tested here provided a useful tool for 1D profiles, but did require additional setup time over film and could not produce 2D dose distributions. However, as diode technology improves, arrays of small closely packed diode SVs 35 , 36 , 37 could be used to produce 2D dose maps in real‐time without the difficulties associated with film.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of the dosimetric properties of a diode detector for small field proton radiosurgery

McAuley

Teran

Slater

et al. 2015

J Applied Clin Med Phys

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The small fields and sharp gradients typically encountered in proton radiosurgery require high spatial resolution dosimetric measurements, especially below 1–2 cm diameters. Radiochromic film provides high resolution, but requires postprocessing and special handling. Promising alternatives are diode detectors with small sensitive volumes (SV) that are capable of high resolution and real‐time dose acquisition. In this study we evaluated the PTW PR60020 proton dosimetry diode using radiation fields and beam energies relevant to radiosurgery applications. Energies of 127 and 157 MeV (9.7 to 15 cm range) and initial diameters of 8, 10, 12, and 20 mm were delivered using single‐stage scattering and four modulations (0, 15, 30, and 60 mm) to a water tank in our treatment room. Depth dose and beam profile data were compared with PTW Markus N23343 ionization chamber, EBT2 Gafchromic film, and Monte Carlo simulations. Transverse dose profiles were measured using the diode in "edge‐on" orientation or EBT2 film. Diode response was linear with respect to dose, uniform with dose rate, and showed an orientation‐dependent (i.e., beam parallel to, or perpendicular to, detector axis) response of less than 1%. Diode vs. Markus depth‐dose profiles, as well as Markus relative dose ratio vs. simulated dose‐weighted average lineal energy plots, suggest that any LET‐dependent diode response is negligible from particle entrance up to the very distal portion of the SOBP for the energies tested. Finally, while not possible with the ionization chamber due to partial volume effects, accurate diode depth‐dose measurements of 8, 10, and 12 mm diameter beams were obtained compared to Monte Carlo simulations. Because of the small SV that allows measurements without partial volume effects and the capability of submillimeter resolution (in edge‐on orientation) that is crucial for small fields and high‐dose gradients (e.g., penumbra, distal edge), as well as negligible LET dependence over nearly the full the SOBP, the PTW proton diode proved to be a useful high‐resolution, real‐time metrology device for small proton field radiation measurements such as would be encountered in radiosurgery applications.PACS numbers: 87.56.‐v, 87.56.jf, 87.56.Fc

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Section: Discussionmentioning

confidence: 99%

Evaluation of the dosimetric properties of a diode detector for small field proton radiosurgery

McAuley

Teran

Slater

et al. 2015

J Applied Clin Med Phys

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“…The pitch (or SV center‐to‐center separation) is 100 μm with a p‐stop implantation between the microstrips (80 μm) for compensation of the accumulation layer generated by irradiation of the thick silicon dioxide 13, 14, 15. A schematic of the DMG SV array is displayed in Fig.…”

Section: Methodsmentioning

confidence: 99%

“…It is a pixelated silicon detector that has the potential to provide not only point dose measurements with a high degree of spatial resolution, but also beam profile measurements in real time. However, while this device has been tested in photon therapy, IMRT, and stereotactic radiotherapy,13, 14, 15 it has yet to be tested in proton therapy. Accordingly, the uniformity of response across the proton spread‐out Bragg peak (SOBP) was unclear.…”

Section: Introductionmentioning

confidence: 99%

Initial testing of a pixelated silicon detector prototype in proton therapy

Wroe

McAuley

Teran

et al. 2017

J Applied Clin Med Phys

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As technology continues to develop, external beam radiation therapy is being employed, with increased conformity, to treat smaller targets. As this occurs, the dosimetry methods and tools employed to quantify these fields for treatment also have to evolve to provide increased spatial resolution. The team at the University of Wollongong has developed a pixelated silicon detector prototype known as the dose magnifying glass (DMG) for real‐time small‐field metrology. This device has been tested in photon fields and IMRT. The purpose of this work was to conduct the initial performance tests with proton radiation, using beam energies and modulations typically associated with proton radiosurgery. Depth dose and lateral beam profiles were measured and compared with those collected using a PTW parallel‐plate ionization chamber, a PTW proton‐specific dosimetry diode, EBT3 Gafchromic film, and Monte Carlo simulations. Measurements of the depth dose profile yielded good agreement when compared with Monte Carlo, diode and ionization chamber. Bragg peak location was measured accurately by the DMG by scanning along the depth dose profile, and the relative response of the DMG at the center of modulation was within 2.5% of that for the PTW dosimetry diode for all energy and modulation combinations tested. Real‐time beam profile measurements of a 5 mm 127 MeV proton beam also yielded FWHM and FW90 within ±1 channel (0.1 mm) of the Monte Carlo and EBT3 film data across all depths tested. The DMG tested here proved to be a useful device at measuring depth dose profiles in proton therapy with a stable response across the entire proton spread‐out Bragg peak. In addition, the linear array of small sensitive volumes allowed for accurate point and high spatial resolution one‐dimensional profile measurements of small radiation fields in real time to be completed with minimal impact from partial volume averaging.

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“…The simulations presented used GEANT4 version 9.3, with physics processes and models recommended by Jarlskog and Paganetti, 18 except for the Livermore low energy electromagnetic physics models, and the addition of G4IonsShenCrossSection cross section implementation to the heavy ion inelastic process. 19 The beam-line was modeled as described in Fig. 4, while the S1 thickness and S2 profile were optimized using the method described above and modeled accordingly in MBEAM.…”

Section: Iif Geant4 Monte Carlo Simulationmentioning

confidence: 99%

Proton beam scattering system optimization for clinical and research applications

et al. 2013

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Independent quality assurance of a helical tomotherapy machine using the dose magnifying glass

Abstract: The DMG with its 0.2 mm spatial resolution coupled to TERA ASIC allowed real-time high temporal resolution measurements of the tomotherapy leaf movement. In conclusion, DMG was shown to be a suitable tool for machine-independent QA of a tomotherapy unit.

Cited by 10 publications

References 12 publications

Evaluation of the dosimetric properties of a diode detector for small field proton radiosurgery

Evaluation of the dosimetric properties of a diode detector for small field proton radiosurgery

Initial testing of a pixelated silicon detector prototype in proton therapy

Proton beam scattering system optimization for clinical and research applications

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