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Use of the 2D MatriXX Detector for Measuring Scanned Ion Beam Parameters

M Varasteh Anvar

M Varasteh Anvar1,2*, S Giordanengo1 , M Donetti1,3 , F Marchetto1 , M Ciocca3 , D Panizza3 , V Monaco1,2 , R Sacchi1,2 , A Vignati1 , L Fanola Guarachi1,2 , R Cirio1,2 , (1) Istituto Nazionale di Fisica Nucleare (INFN), Division of Turin, TO, Italy, (2) University of Torino, Turin, TO, Italy, (3) Centro Nazionale di Adroterapia Oncologica (CNAO), Pavia, PV, Italy


SU-E-T-778 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The quality assurance (QA) procedure has to check the most relevant beam parameters to ensure the delivery of the correct dose to patients. Film dosimetry, which is commonly used for scanned ion beam QA, does not provide immediate results.
The purpose of this work is to answer whether, for scanned ion beam therapy, film dosimetry can be replaced with the 2D MatriXX detector as a real-time tool.

Methods: MatriXX, equipped with 32x32 parallel plate ion-chambers, is a commercial device intended for pre-treatment verification of conventional radiation therapy.
The MatriXX, placed at the isocenter, and GAFCHROMIC films, positioned on the MatriXX entrance, were exposed to 131.44 MeV proton and 221.45 MeV/u Carbon-ion beams.
The OmniPro-I’mRT software, applied for the data taking of MatriXX, gives the possibility of acquiring consecutive snapshots. Using the NI LabVIEW, the data from snapshots were logged as text files for further analysis. Radiochromic films were scanned with EPSON scanner and analyzed using software programs developed in-house for comparative purposes.

Results: The field dose uniformity, flatness, beam position and beam width were investigated. The field flatness for the region covering 6x6 cm² square field was found to be better than 2%. The relative standard deviations, expected to be constant over 2x2, 4x4 and 6x6 pixels from MatriXX measurement gives a uniformity of 1.5% in good agreement with the film results.
The beam center position is determined with a resolution better than 200 μm for Carbon and less than 100 μm for proton beam.
The FWHM determination for a beam wider than 10 mm is satisfactory, whilst for smaller beams the determination is uncertain.

Conclusion: Precise beam position and fast 2D dose distribution can be determined in real-time using MatriXX detector. The results show that MatriXX is quick and accurate enough to be used in charged-particle therapy QA.

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