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Image Quality Through Ultrasound-Compatible Cylinders for Transvaginal Ultrasound-Guided Gynecologic High-Dose-Rate Brachytherapy

D Van Elburg1,2*, M Roumeliotis1,2, A Fenster3,4, J Rodgers3,4, T Meyer1,2, (1) University of Calgary, Calgary, AB, CA, (2) Tom Baker Cancer Centre, Calgary, AB, CA, (3) Robarts Research Institute, London, ON, CA, (4) University of Western Ontario, London, Ontario, CA

Presentations

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

Room: AAPM ePoster Library

Purpose: To evaluate image quality of ultrasound images captured through a sonolucent sheath designed for transvaginal three-dimensional ultrasound (3DUS) guidance in gynecologic HDR brachytherapy.

Methods: The 3DUS system uses a standard bi-plane (transverse and sagittal image planes) cylindrical ultrasound probe on a cradle capable of full 360° rotation. The probe captures incremental 2D sagittal images and reconstructs a 3D image. A sheath (inner diameter 22.1mm, outer diameter 30.0mm) of sonolucent TPX™ plastic (Mitsui Chemicals, Rye Brook, NY. Speed of sound ~2090m/s) houses the probe, which is expected to affect ultrasound images. Image quality with/without the sheath (termed sheath-in and sheath-out) was assessed following AAPM TG-128 recommendations using the CIRS Model 045A Brachytherapy QA Phantom. Sheath-out images were considered baseline.

Results: No significant differences were observed for axial resolution and axial and lateral distance measurements in both image planes. Lateral resolution in the sagittal image plane was 2.1mm and 1.8mm for sheath-in and sheath-out imaging, respectively. Compared to nominal values, sheath-in area (sagittal) and volume (combined sagittal and transverse) measurements increased by 1.7% and 7.0%, respectively. Image depth of penetration decreased by 4.0mm measured from the CIRS phantom surface.

Lateral resolution in the transverse image plane for sheath-in was 2.7mm and 6.0mm in near and far regions, respectively, and 1.5mm and 4.0mm, respectively, for sheath-out. This exceeds the >1mm from baseline tolerance. Transverse image degradation is less concerning since our 3D ultrasound images are reconstructed from sagittal slices. All sagittal tests passed TG-128 tolerances (except volume measurement which involves transverse imaging).

Conclusion: Images acquired through the sonolucent sheath in the sagittal image plane, which is the mode of 3DUS acquisition, are within the AAPM TG-128 tolerance for ultrasound imaging utilized in brachytherapy procedures. Future work includes patient studies evaluating use of 3DUS-based workflows in both intracavitary and interstitial gynecologic HDR brachytherapy.

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Funding Support, Disclosures, and Conflict of Interest: This work is supported by Alberta Innovates and the Alberta Cancer Foundation. Ultrasound equipment provided by Robarts Research Institute at the University of Western Ontario. Potential conflict of interest: co-authors Meyer and Roumeliotis have interest in Okolo Health, a brachytherapy company.

Keywords

Brachytherapy, Ultrasonics, Sonolucent Cylinders

Taxonomy

TH- Brachytherapy: Calibration & Quality Assurance

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