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Evaluation of Fiducial Markers for Radiotherapy Imaging

M Chan

M Chan1*, G Cohen2, J Deasy3, (1) Memorial Sloan-Kettering Cancer Center, Basking Ridge, NJ, (2) Memorial Sloan-Kettering Cancer Center, New York, NY, (3) Memorial Sloan Kettering Cancer Center, New York, NY

SU-D-141-7 Sunday 2:05PM - 3:00PM Room: 141

Purpose: To evaluate visibility, artifacts and distortions of various commercial markers in MRI, CT, and ultrasound imaging used for radiotherapy planning and treatment guidance.

Methods: We compare 2 solid gold markers, 4 gold coils, and 1 polymer marker from 3 vendors. Imaging modalities used were 3T and 1.5T GE MRIs, Siemens Sequoia 512 Ultrasound, Phillips Big Bore CT, Varian Trilogy LINAC (CBCT, OBI-kV, EPID-MV) and Medtronic O-ARM CBCT. Markers were imaged in a 30x30x10cm³ custom bolus phantom. In one experiment, Surgilube™ was used around the markers to reduce air gaps. Images were saved in DICOM format and analyzed using in-house software. Profiles across the markers were used for objective comparison of the markers signals. The visibility and artifacts/distortions produced by each marker were assessed qualitatively and quantitatively.

Results: All markers are visible in CT, CBCT, OBI-kV, and ultrasound. Gold markers below 0.75mm diameter are not visible in EPID-MV images. The larger the markers the more CT and CBCT image artifacts, yet degree of artifact depends on scan parameters. Visibility of gold coils of 0.75mm diameter or larger is comparable across all imaging modalities studied. The polymer marker causes minimal artifacts in CT and CBCT, and has poor visibility in EPID-MV. 0.5mm gold coils exhibit poor visibility in MR and EPID-MV due to their small size. Gold markers are more visible in 3T T1-GRE than in 1.5T T1-SE dependent on the scan sequence. All markers in this study are clearly visible on ultrasound.

Conclusion: When MR and EPID-MV imagers are used, the selection of fiducial markers is not straightforward. For hybrid kV/MV IGRT imaging, larger diameter markers are suggested. If using kV imaging alone, smaller size markers may be used in smaller size of patients in order to reduce artifacts. Only larger diameter gold markers were useful across all imaging modalities.

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