Applicator visualization using ultrashort echo time MRI for high-dose-rate endorectal brachytherapy.

Area of Science:

• Medical Imaging
• Oncology
• Radiotherapy

Background:

• Standard MRI sequences struggle to visualize individual channels in endorectal applicators used for high-dose-rate endorectal brachytherapy.
• Accurate visualization is crucial for precise treatment planning in rectal cancer.

Purpose of the Study:

• To evaluate the efficacy of an ultrashort echo time (UTE) MRI sequence for visualizing individual channels in endorectal applicators.
• To determine the feasibility of using UTE MRI for MR-only treatment planning in rectal cancer.

Main Methods:

• A radial 3D UTE pulse sequence was employed to image phantoms and two rectal cancer patients.
• UTE images were registered with CT scans for applicator phantom analysis.
• Geometric distortion was quantified using a quality assurance phantom and comparing marker positions on UTE and T1-weighted MRI sequences.

Main Results:

• UTE MRI provided sufficient contrast to discern individual channels within the endorectal applicator.
• Channel position differences between UTE and CT were minimal (-0.1 ± 0.1 mm L-R, 0.1 ± 0.3 mm AP).
• Geometric distortion was within acceptable limits (95th percentile ≤ 1.0 mm).

Conclusions:

• UTE MRI adequately visualizes endorectal applicators and their channels in both phantoms and patients.
• The geometrical fidelity of UTE MRI is suitable for MR-only treatment planning in rectal cancer brachytherapy.