4 years ago

Improvement of single detector proton radiography by incorporating intensity of time-resolved dose rate functions.

Hsiao-Ming Lu, Ethan W Cascio, Rongxiao Zhang, Gregory C Sharp, Jacob B Flanz, Kyung-Wook Jee
Proton radiography, which images patients with the same type of particles as what they are to be treated with, is a promising approach to image guidance and water equivalent path length (WEPL) verification in proton radiation therapy. We have shown recently that proton radiographs could be obtained by measuring time-resolved dose rate functions (DRF) using an x-ray amorphous silicon flat panel. The WEPL values were derived solely from the root-mean-square (RMS) of DRFs while the intensity information in the DRFs was filtered out. In this work, we explored the use of such intensity information for potential improvement in WEPL accuracy and imaging quality. Three WEPL derivation methods based on, respectively, the RMS only, intensity only, and the intensity weighted RMS were tested and compared in terms of the quality of obtained radiograph images and the accuracy of WEPL values. A Gammex CT calibration phantom containing inserts made of various tissue substitute materials with independently measured relative stopping powers (RSP) were used to assess the imaging performances. Improved image quality with enhanced interfaces was achieved while preserving the accuracy by utilizing intensity information in the calibration. Other objects including an anthropomorphic head phantom, a proton therapy range compensator, a frozen lamb head and an "image quality phantom" were also imaged. Both RMS only and intensity weighted RMS methods derived the RSPs within ± 1% for most of the Gammex phantom inserts, with the mean absolute percentage error of 0.66% for all inserts. In the case of the insert with a titanium rod, the method based on RMS completely failed whereas that based on intensity weighted RMS was qualitatively valid. The use of intensity greatly enhanced the interfaces between different materials in the obtained WEPL images, suggesting the potential for image guidance such as patient positioning and tumor tracking by proton radiography.

Publisher URL: http://doi.org/10.1088/1361-6560/aa9913

DOI: 10.1088/1361-6560/aa9913

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