Skin marker for MR-only surface high-dose-rate brachytherapy.

Area of Science:

• Medical Imaging
• Radiation Oncology
• Biomaterials

Background:

• Surface high-dose-rate (HDR) brachytherapy requires accurate visualization of clinical targets, including human skin and fibromatosis.
• Current workflows rely on markers detectable by both MRI and CT, but existing MR markers are unsuitable for continuous surface target tracing.
• Complete MR-only workflows necessitate reliable skin markers for defining clinical target edges.

Purpose of the Study:

• To evaluate silicone rubber tubes as an alternative skin marker for MRI and CT detectability and contourability in brachytherapy.
• To assess the suitability of these markers for MR-only surface HDR brachytherapy workflows.

Main Methods:

• Silicone rubber tubes (2-3 mm diameter) were applied to phantoms, volunteers, and patients with palmar fibromatosis.
• Imaging was performed using optimized 3D PETRA and VIBE sequences with Dixon reconstruction, alongside standard CT.
• Tube detectability, conspicuity, and contouring accuracy were evaluated using a brachytherapy treatment planning system (TPS) and contouring software.

Main Results:

• Silicone rubber tubes were successfully detected on PETRA, VIBE (especially Dixon VIBE fat-only), and CT images.
• 3 mm diameter tubes demonstrated better tracking in the TPS compared to 2 mm tubes.
• MR imaging in three orthogonal planes improved tube localization within the TPS.
• Contour shapes derived from the markers generally agreed with known tube positions.

Conclusions:

• Solid silicone rubber tubes, particularly 3 mm in diameter, are suitable skin markers for MR-only surface HDR brachytherapy.
• These markers offer a viable alternative to traditional CT markers, facilitating complete MR-only treatment planning.