Technical note| Volume 107, 102561, March 2023

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Characterization of a flat-panel detector for 2D dosimetry in scanned proton and carbon ion beams

Published:March 08, 2023DOI:


      • Daily QA is of utmost importance in particle therapy due to the workflow complexity.
      • The Sphinx Compact can fasten the daily QA procedures in particle therapy.
      • Quenching effect is an issue for the Sphinx Compact, 3D measurements are discouraged.
      • The Sphinx Compact can be a useful and time-saving tool for constancy checks.



      To fully characterize the flat panel detector of the new Sphinx Compact device with scanned proton and carbon ion beams.

      Materials and methods

      The Sphinx Compact is designed for daily QA in particle therapy. We tested its repeatability and dose rate dependence as well as its proportionality with an increasing number of particles and potential quenching effect. Potential radiation damage was evaluated. Finally, we compared the spot characterization (position and profile FWHM) with our radiochromic EBT3 film baseline.


      The detector showed a repeatability of 1.7% and 0.9% for single spots of protons and carbon ions, respectively, while for small scanned fields it was inferior to 0.2% for both particles. The response was independent from the dose rate (difference from nominal value < 1.5%). We observed an under-response due to quenching effect for both particles, mostly for carbon ions. No radiation damage effects were observed after two months of weekly use and approximately 1350 Gy delivered to the detector. Good agreement was found between the Sphinx and EBT3 films for the spot position (central-axis deviation within 1 mm). The spot size measured with the Sphinx was larger compared to films. For protons, the average and maximum differences over different energies were 0.4 mm (3%) and 1 mm (7%); for carbon ions they were 0.2 mm (4%) and 0.4 mm (6%).


      Despite the quenching effect the Sphinx Compact fulfills the requirements needed for constancy checks and could represent a time-saving tool for daily QA in scanned particle beams.


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      1. PTCOG – Facilities in Operation n.d. (accessed November 15, 2021).

        • Uhl M.
        • Herfarth K.
        • Debus J.
        Comparing the use of protons and carbon ions for treatment.
        Cancer J. 2014; 20: 433-439
        • Arjomandy B.
        • Taylor P.
        • Ainsley C.
        • Safai S.
        • Sahoo N.
        • Pankuch M.
        • et al.
        AAPM task group 224: Comprehensive proton therapy machine quality assurance.
        Med Phys. 2019; 46
        • Bizzocchi N.
        • Fracchiolla F.
        • Schwarz M.
        • Algranati C.
        A fast and reliable method for daily quality assurance in spot scanning proton therapy with a compact and inexpensive phantom.
        Med Dosim. 2017; 42: 238-246
        • Actis O.
        • Meer D.
        • König S.
        • Weber D.C.
        • Mayor A.
        A comprehensive and efficient daily quality assurance for PBS proton therapy.
        Phys Med Biol. 2017; 62: 1661-1675
        • Rana S.
        • Samuel E.J.J.
        Feasibility study of utilizing XRV-124 scintillation detector for quality assurance of spot profile in pencil beam scanning proton therapy.
        Phys Medica. 2019; 66: 15-20
        • Cook H.
        • Lambert J.
        • Thomas R.
        • Palmans H.
        • Hussein M.
        • Clark C.H.
        • et al.
        Development of a heterogeneous phantom to measure range in clinical proton therapy beams.
        Phys Medica. 2022; 93: 59-68
        • Almurayshid M.
        • Helo Y.
        • Kacperek A.
        • Griffiths J.
        • Hebden J.
        • Gibson A.
        Quality assurance in proton beam therapy using a plastic scintillator and a commercially available digital camera.
        J Appl Clin Med Phys. 2017; 18: 210-219
        • Russo S.
        • Mirandola A.
        • Molinelli S.
        • Mastella E.
        • Vai A.
        • Magro G.
        • et al.
        Characterization of a commercial scintillation detector for 2-D dosimetry in scanned proton and carbon ion beams.
        Phys Medica. 2017; 34: 48-54
        • Varasteh Anvar M.
        • Attili A.
        • Ciocca M.
        • Donetti M.
        • Fanola Guarachi L.K.
        • Fausti F.
        • et al.
        Quality assurance of carbon ion and proton beams: a feasibility study for using the 2D MatriXX detector.
        Phys Medica. 2016; 32: 831-837
        • Decabooter E.
        • Roijen E.
        • Martens J.
        • Unipan M.
        • Bosmans G.
        • Vilches-Freixas G.
        Quality assurance of scanned proton beams at different gantry angles using an ionization chamber array in a rotational phantom.
        Phys Medica. 2022; 104: 67-74
        • Vai A.
        • Mirandola A.
        • Magro G.
        • Maestri D.
        • Mastella E.
        • Mairani A.
        • et al.
        Characterization of a MLIC detector for QA in scanned proton and carbon ion beams.
        Int J Part Ther. 2019; 6: 50-59
        • Kozicki M.
        • Maras P.
        Features of 2Day.QA® as a 2D radiation dosimeter.
        Phys Medica. 2022; 104: 23-31
        • Lambert J.
        • Bäumer C.
        • Koska B.
        • Ding X.
        Daily QA in proton therapy using a single commercially available detector.
        J Appl Clin Med Phys. 2014; 15: 217-228
        • Mirandola A.
        • Molinelli S.
        • Vilches Freixas G.
        • Mairani A.
        • Gallio E.
        • Panizza D.
        • et al.
        Dosimetric commissioning and quality assurance of scanned ion beams at the Italian National Center for Oncological Hadrontherapy.
        Med Phys. 2015; 42: 5287-5300
      2. Menzel H-G. International Commission on Radiation Units and Measurements. vol. 15. 2015. doi: 10.1093/jicru_ndy011.

        • Castriconi R.
        • Ciocca M.
        • Mirandola A.
        • Sini C.
        • Broggi S.
        • Schwarz M.
        • et al.
        Dose-response of EBT3 radiochromic films to proton and carbon ion clinical beams.
        Phys Med Biol. 2017; 62: 377-393
        • Holm K.M.
        • Yukihara E.G.
        • Ahmed M.F.
        • Greilich S.
        • Jäkel O.
        Triple channel analysis of Gafchromic EBT3 irradiated with clinical carbon-ion beams.
        Phys Medica. 2021; 87: 123-130
        • Hartmann B.
        • Telsemeyer J.
        • Huber L.
        • Ackermann B.
        • Jäkel O.
        • Martišíková M.
        Investigations of a flat-panel detector for quality assurance measurements in ion Beam Therapy.
        Phys Med Biol. 2012; 57: 51-68
        • Placidi L.
        • Togno M.
        • Weber D.C.
        • Lomax A.J.
        • Hrbacek J.
        Range resolution and reproducibility of a dedicated phantom for proton PBS daily quality assurance.
        Z Med Phys. 2018; 28: 310-317
        • Su Z.
        • Hsi W.
        • Forthomme J.
        • Rossomme S.
        Evaluations of a flat-panel based compact daily quality assurance device for proton pencil beam scanning (PBS) system.
        Phys Med. 2020; 80: 243-250
        • Rossi S.
        The National Centre for Oncological Hadrontherapy (CNAO): status and perspectives.
        Phys Med. 2015; 31: 333-351
        • Giordanengo S.
        • Garella M.A.
        • Marchetto F.
        • Bourhaleb F.
        • Ciocca M.
        • Mirandola A.
        • et al.
        The CNAO dose delivery system for modulated scanning ion beam radiotherapy.
        Med Phys. 2015; 42: 263-275
        • Vignati A.
        • Hosseini S.M.A.
        • Attili A.
        • Ciocca M.
        • Donetti M.
        • Giordanengo S.
        • et al.
        Accuracy assessment of the CNAO dose delivery system in the initial period of clinical activity and impact of later improvements on delivered dose distributions.
        Med Phys. 2020; 47: 1468-1480
        • Mirandola A.
        • Magro G.
        • Lavagno M.
        • Mairani A.
        • Molinelli S.
        • Russo S.
        • et al.
        Characterization of a multilayer ionization chamber prototype for fast verification of relative depth ionization curves and spread-out-Bragg-peaks in light ion beam therapy.
        Med Phys. 2018; 45: 2266-2277
        • Mirandola A.
        • Magro G.
        • Maestri D.
        • Mairani A.
        • Mastella E.
        • Molinelli S.
        • et al.
        Determination of ion recombination and polarity effect correction factors for a plane-parallel ionization Bragg peak chamber under proton and carbon ion pencil beams.
        Phys Med Biol. 2019; 64: 095010
        • Martišíková M.
        • Hartmann B.
        • Hesse B.M.
        • Brons S.
        • Ackermann B.
        • Jäkel O.
        Characterization of a flat-panel detector for ion beam spot measurements.
        Phys Med Biol. 2012; 57: 485-497