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.
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.