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Development of Multi-Layer/strip Ionization Chamber Array for Proton Pencil Beam Scanning Field Delivery Verification

s zhou1*, T Zhao1 , B Sun1 , S Mutic1 , L Lin2 , T Zhang1 , (1) Washington University School of Medicine, Saint Louis, MO, (2)Emory Proton Therapy Center, Atlanta, GA


(Wednesday, 7/17/2019) 7:30 AM - 9:30 AM

Room: 303

Purpose: Intensity modulated proton therapy (IMPT) deliveries non-uniform dose distribution that needs to be verified before treatments. Measurement of treatment fields using film or 2D detector array is tedious and only provide partial dose information. The purpose of this study is to develop a quality assurance (QA) device for convenient pencil beam scanning (PBS) delivery verification.

Methods: The multilayer ionization chamber array comprises of two layers of strip ionization chambers plates for spot position (x, y) measurement and 64 layers of plate ionization chambers for depth (z) measurement. The spatial resolution of the strip detector is 2mm and maximum field size coverage is 25.6 cm. The data acquisition system comprises of 512-channel analog-to-digital (A/D) converters that integrate and sample all channels at maximum speed of 3.125 kHz. Matlab programs were developed to analyze and display the beam data.

Results: Relative detection sensitivities of x-y channels and z-channels were calibrated. The profile and depth dose curves of various double scattering beams were sampled for about 4s integration. The raw data are corrected for background and relative sensitivity. Water equivalent thickness of each chamber layer was measurement at about 1.905 mm. The multilayer ion chamber is able to measure beam profile and range with sub-millimeter accuracy after calibration.

Conclusion: Multilayer ionization chamber array is successfully developed. It can measure spot position and depth with ultra-fast sampling speed. It can be a convenient tool for IMPT QA measurement and potentially can be used as a proton portal imaging device.


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