Presentation A real-time single-shot energy subtraction image filter for markerless tumor tracking in radiotherapy

森, 慎一郎

Purpose:To improve markerless tumor tracking accuracy in radiotherapy, we developed the energy subtraction (ES) image filter by a single shot x-ray exposure.Methods:The ES filter consisted of a 2-mm thickness steel-use-stainless and 128 pairs slits shape (0.388-mm width and space). It was set on the front of the dynamic flat panel detector (DFPD). DFPD pixel size is 0.388 mm. Chest phantom was set on the couch and acquired DFPD images. Acquisition conditions were 120 kV of tube voltage, 20 mA of tube current and 4 ms of exposure. 20 images were averaged to improve image quality. DFPD image was separated into columns with and without slits. Pixels with slits were interpolated by adjacent pixels without slits. Similarly, those without slits were interpolated by adjacent pixels with slits. By doing this, both images were filled with pixels with and without slits in the original image size. Energy subtraction image was calculated by subtracting both images.Results:Energy subtraction image for the chest phantom was successfully obtained by a single shot exposure with ES filter. Bone structures were removed. Calculation time was less than a few milliseconds. However, imager contrast was degraded due to ES filter setup error and/or ES filter manufacturing accuracy.Conclusions: The ES filter provided good bone suppression image in a real-time and could be useful for markerless tumor tracking.

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