PHSPP06 Presentation Time: 3:20 PM

Purpose

Brachytherapy applicator conspicuity during ultrasound (US) imaging can be impaired by bowel gas, tissue interfaces, or when the applicator is far or angled with respect to the ultrasound probe. Without adequate conspicuity, applicators can be inaccurately reconstructed, leading to decreased tumor control or increased normal tissue dose due to a geometrically inaccurate treatment plan. To improve the conspicuity of titanium high-dose rate (HDR) brachytherapy needles under US imaging, the surface of needles can be modified, and color-Doppler can be utilized to highlight the surface patterns. Color-Doppler imaging can produce a twinkling signature, also referred to as a ‘twinkling artifact,' when ultrasound waves reflect from a surface with a rough or patterned structure. The twinkling signature highlights the modified applicator as variegated pixels atop a grayscale B-mode US image, enhancing conspicuity. This research was a preliminary investigation into the types of surface modifications that can produce a twinkling signature, based upon a review of prior literature that has associated surface roughness with twinkling.

Materials and Methods

The surfaces of 17-gauge, 25 cm titanium HDR brachytherapy needles were modified using three methods of surface modification: sandblasting with an 80-grit media, laser-etching of thin grooves, and application of a polymethyl methacrylate (PMMA)-based bone cement. Laser-etches were created on the surface of the needles using a 343 nm femtosecond laser (Pharos, Light Conversion, Lithuania) on a machining system (Photomachining Inc., USA) and were created at variable widths (0.1-1 mm) and depths (10-100 μm) without penetrating the inner lumen of the applicator. Unmodified and modified needles were imaged with a bk3000 (BK Medical, USA) with an E14CL4b transrectal probe and Logiq E9 (General Electric, USA) with a 9L linear-array transducer under B-mode and color-Doppler imaging. Needle conspicuity between needle types was assessed qualitatively in the axial and sagittal planes within a prostate phantom (CIRS, Inc., USA).

Results

Color-Doppler imaging in combination with surface-modified needles produced a twinkling signature with select laser-etched and PMMA-cement surface modifications. The twinkling signature appeared as a color signal atop the applicator, overlaid on grayscale B-mode ultrasound images. The twinkling signature was observed with both transrectal and linear-array ultrasound transducers. Twinkling was observed at laser-etched scribe depths >20 μm and widths >0.1 mm, and it was observed that the magnitude of the twinkling signature was dependent upon the total surface area of the etched region. It was also demonstrated that needles can be laser-etched or coated with PMMA-cement to mark a reference location with respect to the needle tip (2 cm distal). The hand-roughened needles produced a faint twinkling signature with the linear-array transducer and negligible twinkling with the transrectal transducer. Sandblasted and unmodified needles produced a negligible twinkling signature. Generally, the twinkling signature was observed to be transient in nature and dependent on the pressure between the probe and the phantom. Future work is planned to study the mechanisms underlying the color-Doppler signal and to establish an optimal surface modification and signal strength.

Conclusions

Color-Doppler ultrasound combined with brachytherapy applicator surface modifications may be used to enhance applicator conspicuity and aid with applicator placement and digitization. HDR brachytherapy needles may be modified for color-Doppler imaging via laser-etching or coating with a PMMA-based bone cement.