1. Short Arc Digital Tomosynthesis as an Image Enhancement Step for Detection and Localization of Implanted Markers Margie Hunt, Pengpeng Zhang Memorial Sloan-Kettering Cancer Center, New York NY Hassan Mostafavi, Alexander Sloutsky, Andrew Jeung Varian Medical Systems Inc., Palo Alto CA

2. Automatic detection of implanted radio-opaque markers can be challenging due to noise, scatter, and obfuscating structures Image enhancement by Short Arc Digital Tomosynthesis (DTS) – tomosynthesis reconstruction over a 3 – 5° arc – may enhance images to aid detection Enhancement can be quantified by matching to an image template and calculating the peak-to-sidelobe ratio (PSR) of the resulting match surface Study Objectives

3. Image Enhancement using Short Arc DTS  Example scenario: Gantry rotation during treatment e.g. RapidArc  Use MV projections over last θ degrees to reconstruct a DTS image  Targets that would otherwise be obscured by scatter noise and overlaying structures will be enhanced sufficiently for successful automatic tracking

4. Results Comparison of original MV images (left) to DTS-enhanced images (right). DTS- enhanced markers are easier to identify, and band artifacts due to linac are eliminated. a b PSR = 5.812 c PSR = 8.251 Template of markers generated from plan CT (a) matches with the DTS-enhanced image (c) with a higher PSR score than with the original MV projection (b).

5. Gantry Angle PSR: Template to original image PSR: Template to DTS- enhanced image 21.3°5.8128.251 49.0°3.0075.666 81.0°3.0313.734 DTS enhancement results in a consistently higher peak-to-sidelobe ratio (PSR)

6. Conclusions Short Arc DTS can enhance image sequences acquired during gantry rotation It shows promise in making detection and localization of markers more robust and accurate Template matching and use of peak-to-sidelobe ratio can quantify the improvement in detectability