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Implications of Metallic Spine Hardware On Dosimetry and Image Verification in Spine SBRT

E Tchistiakova*, H Morrison, K Thind, N Ploquin, Tom Baker Cancer Center, Calgary, AB,CA

Presentations

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

Room: AAPM ePoster Library

Purpose: quantify the impact of metallic fixations used in surgical spine stabilization on radiation dosimetry and CBCT image quality in spine SBRT.


Methods: A phantom was created using a 3D-printed spine model with implanted rods and screws and submerged in an organic gelatin. A CT scan of the phantom was acquired using a clinical Spine SBRT protocol. A radiation oncologist contoured a GTV/PTV based on spine SBRT guidelines.

Dosimetry:
A base treatment plan was created using Eclipse and optimized using the AAA model. It was compared to the Acuros calculated dose with assigned materials and densities for the rods and screws of stainless steel (8.0 g/cm3) and titanium alloy (4.42 g/cm3), respectively.
AAA and Acuros calculated doses were also compared to EBT3 GafChromic film measurements.

CBCT image quality:
Pelvis and Thorax protocols were investigated with 1 standard and 5 advanced iterative CBCT reconstruction techniques (Varian Medical Systems).
High and low density artifact analysis was performed on the six image sets to evaluate image quality.

Results:
Dosimetry:
AAA and Acuros agreed within <2% and with gamma pass rates of 100% at 3%/1mm and 90% at 1%/1mm within clinically relevant regions. The average local dose differences between film and AAA/Acuros were 1.6%/0.5% and gamma pass rates were 99.7%/99.8% at 3%/1mm and 98.5%/96.5% at 1%/1mm, respectively.

CBCT image quality:
Standard reconstruction had the highest contribution of high and low density artifacts for both protocols. Comparison of 5 iCBCT reconstruction techniques showed marginal benefit, with higher artifact reduction when using Smoothing Filter with Very High noise suppression and Adaptive detruncation volume.

Conclusion: Spinal hardware had minimal clinical impact on the accuracy of both AAA and Acuros. iCBCT reconstruction was beneficial for artifact reduction compared to standard reconstruction.

Download ePoster [PDF]

Keywords

Dosimetry, Image Artifacts, Stereotactic Radiosurgery

Taxonomy

IM/TH- Cone Beam CT: Image Reconstruction

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