KEY POINTS
- This technical note developed an electromagnetic tracking system for live guidance during gynecologic brachytherapy. It was evaluated in a commercial phantom and subsequently tested during combined intracavitary–interstitial implants in two patients with cervical cancer.
- The platform combined a freehand, stepper-less transrectal ultrasound probe with a preacquired magnetic resonance image, magnetic resonance-based contours, and a tracked stylet placed inside the active interstitial needle.
- Across 20 phantom registrations, magnetic resonance imaging–ultrasound fusion error averaged 3.9 ± 1.3 mm. Needle-display accuracy averaged 2.4 ± 0.9 mm immediately after calibration and 4.7 ± 1.9 mm when a previously defined calibration was used in a new setup.
- During the two clinical implants, fusion accuracy remained within 4 mm and needle-localization accuracy within 5 mm despite probe translation, rotation, removal, and reinsertion. Magnetic resonance imaging–ultrasound registration, including fine adjustment, took less than 5 minutes.
- The system used rigid registration and axial ultrasound only. It did not support treatment planning or catheter reconstruction, and its clinical evaluation did not assess implant dosimetry, procedural complications, or patient outcomes.
CLINICAL TAKEAWAY
Electromagnetic tracking may make preacquired magnetic resonance imaging information and interstitial needle position available during live ultrasound-guided gynecologic brachytherapy without requiring a fixed probe stepper. However, the system remains an early technical implementation evaluated in only two patients and requires broader validation before routine clinical adoption.