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Highly Efficient Synchronized High-Speed Scintillation Camera System for Measuring Proton Range, SOBP and Dose Distributions in a 2D-Plane

S Goddu

S Goddu*, B Sun , K Grantham , T Zhao , T Zhang , J Bradley , S Mutic , Washington University School of Medicine, Saint Louis, MO


TH-CD-201-10 (Thursday, August 4, 2016) 10:00 AM - 12:00 PM Room: 201

Proton therapy (PT) delivery is complex and extremely dynamic. Therefore, quality assurance testing is vital, but highly time-consuming. We have developed a High-Speed Scintillation-Camera-System (HS-SCS) for simultaneously measuring multiple beam characteristics.

High-speed camera was placed in a light-tight housing and dual-layer neutron shield. HS-SCS is synchronized with a synchrocyclotron to capture individual proton-beam-pulses (PBPs) at ~504 frames/sec. The PBPs from synchrocyclotron trigger the HS-SCS to open its shutter for programmed exposure-time. Light emissions within 30x30x5cm3 plastic-scintillator (BC-408) were captured by a CCD-camera as individual images revealing dose-deposition in a 2D-plane with a resolution of 0.7mm for range and SOBP measurements and 1.67mm for profiles. The CCD response as well as signal to noise ratio (SNR) was characterized for varying exposure times, gains for different light intensities using a TV-Optoliner system. Software tools were developed to analyze ~5000 images to extract different beam parameters. Quenching correction-factors were established by comparing scintillation Bragg-Peaks with water scanned ionization-chamber measurements. Quenching corrected Bragg-peaks were integrated to ascertain proton-beam range (PBR), width of Spared-Out-Bragg-Peak (MOD) and distal dose-fall-off. Summed-Images were used to determine off-axis-dose profiles, flatness and symmetry (F&S), beam-divergence and isodose-distributions.

Monitor-units linearity experiments revealed that the HS-SCS is capable of capturing all PBPs. Several PBR and modulation-width combinations were tested and the measured range and MOD were fond to be within ±2mm. The system is capable of extracting F&S from dose profiles as well as isodose distributions in 2D-planes. This system can also be used to range compensator verification.

This preliminary data demonstrates that the HS-SCS is capable of simultaneously measuring several different beam-parameters. Novelty of this tool is its efficiency and ability to analyze individual PBPs to ascertain critical parameters of the proton beams. This system can be used for QA of both passive scattering and pencil-beam-scanning systems.

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