KEY POINTS
- Investigators developed a motorized attachment for the commercially available CIVCO EX3 stepper to automate sagittal 3D transrectal ultrasound acquisition during prostate HDR brachytherapy planning.
- Manual and motorized acquisitions were compared across rotation speeds. Motorized scans ranged from 2 to 10°/s, while manual scans ranged from 4.2 to 27.5°/s, with image quality assessed using PSNR, SSIM and MS-SSIM against an ideal reference acquisition.
- Motorized imaging consistently produced greater similarity to the reference than manual acquisition. The fastest motorized scan at 10°/s achieved the best average image-similarity metrics despite requiring only 13 seconds versus 23 seconds for the slowest manual acquisition.
- Mean axial resolution, elevational resolution, distance error and volume error did not differ significantly between acquisition methods. The advantage of motorization was primarily improved consistency rather than a large shift in mean accuracy.
- Manual scanning showed significantly greater variability in elevational distance error (p=0.0081) and volume measurement error (p<0.0001). Motorized acquisition substantially narrowed this scan-to-scan variability.
- Operator dependence was also reduced. Manual acquisition produced significant differences between operators for elevational distance error (p=0.0271), axial distance error (p=0.0433) and volume error (p=0.0226), while none of these metrics differed significantly between operators with motorized acquisition.
- Qualitative phantom imaging showed a smoother prostate boundary and more clearly defined urethral geometry after motorized acquisition, while manually acquired images contained visible brightness and reconstruction artifacts caused by non-uniform probe rotation.
- The study was performed entirely in phantoms, used only three motorized and three manual quantitative scans per operator, and manual acquisitions were not performed by an experienced clinical operator. Whether the improvement translates into better needle localization or dosimetry in patients remains unknown.
CLINICAL TAKEAWAY
Motorizing sagittal 3D ultrasound acquisition may remove an avoidable source of operator-dependent variability in prostate HDR brachytherapy planning. The engineering solution is practical and potentially workflow-relevant, but patient-level validation is needed before a dosimetric or clinical benefit can be claimed.