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Detectability of MR Suitable Prostate Fiducial Markers in An Anthropomorphic Phantom Utilizing the TrueBeam Advanced Imaging Package During VMAT Prostate Treatment

M Klem1*, K Jones2, J Turian3, (1) Rush University Medical Center, Chicago, IL (2) Rush University Medical Center, Chicago, IL, (3) Rush University Medical Center, Chicago, IL


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Prostate treatment planning requires prostate fiducial markers (FM) to be visible in MR and X-ray images. We compare the detectability of MR suitable gold and platinum FM’s, by Varian TrueBeam’s Advanced Imaging Package during VMAT prostate treatment of a stationary anthropomorphic phantom, to that of polymer-based markers currently in clinical use.

Phantom experiments were performed with a Rando phantom holding a beefsteak prostate phantom. Gold-based-segmented (0.4x10mm), platinum-coil (0.5x5mm), and polymer-based-cylindrical (1x3mm) fiducial markers were implanted into the prostate phantom. The phantom received (VMAT) therapy utilizing on-board kV imaging. In each image, the Varian software detected the presence and location of each marker within a 3mm radius of its planned location. Treatment was repeated 11 times using different marker detection settings (MDS) to collect 484 images. MR images were collected to assess MR suitability.

Accurate detection varied widely with MDS. “GoldSeed_1_0x2_0” was most robust to all MDS.
The best MDS for the gold and polymer markers was “GoldSeed_1_0x2_0”. “GoldSeed_1_0x2_5” was best for platinum.

Positive localization (PL) inversely correlated with marker setting length (MSL) (r =-0.78). Negative detection (ND) correlated with MSL (r=0.80). Negative localization (NL) correlated with MSL (r =0.26).
Using optimized MDS per marker, PL rates for gold/platinum/polymer were 95.5%,95.5%,79.5%. NL rates for gold/platinum/polymer markers were 0.0%,0.0%,0.0%. ND rates for gold/platinum/polymer markers were 0.0%,0.0%,15.9%.

MRI CNR of gold and platinum markers was 18% better compared to polymer markers.

Periodic kV imaging and automatic marker detection during VMAT prostate treatments is used to assess the detectability of three MR suitable fiducial markers. Gold and platinum markers show improved detectability compared to polymer markers. The effect of motion on marker detectability is currently being assessed.


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