# Feasibility of 3D-Printed Brachytherapy Contrast Markers for Use With CT Planning of Interstitial Procedures

## TL;DR

This study shows that 3D-printed markers made with copper-infused plastic can be used for brachytherapy planning and offer better visibility and fewer imaging artifacts than traditional metal markers.

## Contribution

The novelty lies in demonstrating 3D-printed, metal-infused markers as a cost-effective and MR-safe alternative for brachytherapy with reduced CT artifacts.

## Key findings

- Solid copper PLA markers had higher contrast-to-noise ratios than steel and nitinol markers in both tissue and air environments.
- 3D-printed markers showed significantly lower CT metal artifacts compared to commercial metal markers.
- Hollow markers allowed for dual contrast media testing, enabling potential use in both CT and MRI.

## Abstract

Background

Interstitial brachytherapy needles utilize radio-opaque markers that are expensive, not MR-safe, and have significant artifacts on CT/MRI. Here, we demonstrate the feasibility of 3D-printed radio-opaque markers composed of metal-infused polylactic acid (PLA) and test their use on CT-based localization of interstitial brachytherapy needles.

Methodology

Radio-opaque markers were 3D-printed using PLA filament infused with copper. Solid and hollow markers were designed, with hollow markers capable of containing viscous contrast media. Hollow markers were constructed heterogeneously with a single stripe of copper PLA along the length of a metal-free PLA to allow for feasibility testing of detecting dual contrast media using both CT and MRI. Markers were imaged via CT inside a prostate phantom and compared directly against steel and nitinol markers. Comparisons were performed in both soft tissue and air density regions. CT metal artifact (CTMA) was computed via standard deviation in the volume around each marker. Contrast-to-noise ratios (CNRs) were evaluated using CT imaging for all tested markers using identical methodology. Artifact differences between markers were compared by evaluating the standard deviations of fixed volumes around each voxel.

Results

The average CNR for solid and hollow copper PLA markers was 1.99 ± 0.07 and 1.23 ± 0.21 in tissue and 2.48 ± 0.10 and 2.99 ± 0.15 in air, respectively. The average CNR for wire and nitinol markers was 1.31 ± 0.02 and 2.33 ± 0.05 in tissue and 1.86 ± 0.01 and 2.76 ± 0.01 in air, respectively. CTMA for solid and hollow copper PLA markers were 13.62 and 8.80 HU in tissue and 9.99 and 13.66 HU in air, respectively. The average artifact for the nitinol and wire markers was 75.93 and 18.06 HU in tissue and 50.71 and 16.64 HU in air, respectively.

Conclusions

Solid copper PLA 3D-printed markers have superior visibility to commercially available steel marker wires. Both types of printed markers exhibited reduced imaging artifacts when compared with commercially available markers. Printed markers can improve the accuracy of interstitial planning and can be inexpensively produced in-house.