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

• 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

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

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).

Gantry AnglePSR:

Template to original image

PSR:Template to

DTS-enhanced

image

21.3° 5.812 8.251

49.0° 3.007 5.666

81.0° 3.031 3.734

DTS enhancement results in a consistently higher peak-to-sidelobe ratio (PSR)

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