PURPOSE: The success of radiation therapy for lung cancer treatment is limited by tumor motion during breathing and thus the ability to target effectively. Real-time localization and tracking may enable increased tumor radiation and decreased healthy tissue irradiation. Real-time localization of implanted gold fiducials is limited by high doses of non-therapeutic imaging radiation, expensive fluoroscopic equipment, subjective image interpretation and poor implant stability. A real-time, non-ionizing, objective, electromagnetic localization system that uses wireless implanted Beacon® transponders has been developed (Calypso Medical, Seattle, WA). We compared bronchoscopic implant feasibility and stability for both transponders and gold fiducials in peripheral airways of canine lungs.
METHODS: Following approval of the Animal Care and Use Committee, five mongrel dogs (weight = 20.3 ± 1.4 kg) were anesthetized, intubated, and ventilated (pressure support between 0 and 20 cm H2O). Three Beacon transponders (1.8 mm × 8.5 mm) were inserted into the tip of a plastic catheter with an inner wire releasing plunger, passed through the 2.6 mm working channel of a flexible bronchoscope (Olympus® America Inc., Melville, NY), and implanted into small sub-segmental bronchi of a single lobe using fluoroscopic guidance. This procedure was repeated for three spherical gold markers (diameter 2.0 mm) in the opposite lung. At one day, two weeks and one month following implantation, fluoroscopy and electromagnetic tracking were used to assess implant stability.
RESULTS: Successful bronchoscopic implantation was possible for 15/15 transponders and 12/15 gold fiducials; 3 gold fiducials were implanted in the pleural space. One day after implantation 15/15 successfully implanted transponders and 12/12 successfully implanted gold fiducials remained. At 2 weeks for 4 animals and 1 month for one animal 10/15 (66%) transponders and 8/12 (66%) gold spheres remained.
CONCLUSION: Bronchoscopic implantation of both transponders and gold fiducials into the small peripheral airways of the canine lung is feasible. Future work will focus on transponder retention in lung tissue.
CLINICAL IMPLICATIONS: Implantable electromagnetic transponders may allow improved radiation therapy for lung cancer by providing real-time continuous target tracking.
DISCLOSURE: Martin Mayse, Consultant fee, speaker bureau, advisory committee, etc. Consultant, Calypso Medical Technologies, Inc.; Product/procedure/technique that is considered research and is NOT yet approved for any purpose, Implantation of electromagnetic transponders in the lung.