CLINICAL INVESTIGATION Lung BRONCHOSCOPIC IMPLANTATION OFA NOVEL WIRELESS ELECTROMAGNETIC TRANSPONDER IN THE CANINE LUNG: A FEASIBILITY STUDY MARTIN L. MAYSE, M.D.,* PARAG J. PARIKH, M.D., y KRISTEN M. LECHLEITER, B.S., y STEVEN DIMMER, B.S., z MIA PARK, M.S., z AMIR CHAUDHARI, M.S., y MICHAEL TALCOTT, D.V.M., x DANIEL A. LOW,PH.D., y AND JEFFREY D. BRADLEY, M.D. y * Division of Pulmonary and Critical Care; y Department of Radiation Oncology, x Division of Comparative Medicine, Washington University School of Medicine, St. Louis, MO; and z Calypso Medical Technologies, Seattle, WA Purpose: The success of targeted radiation therapy for lung cancer treatment is limited by tumor motion during breathing. A real-time, objective, nonionizing, electromagnetic localization system using implanted electromag- netic transponders has been developed (Beacon electromagnetic transponder, Calypso Medical Technologies, Inc., Seattle, WA). We evaluated the feasibility and fixation of electromagnetic transponders bronchoscopically implanted in small airways of canine lungs and compared to results using gold markers. Methods and Materials: After approval of the Animal Studies Committee, five mongrel dogs were anesthetized, intubated, and ventilated. Three transponders were inserted into the tip of a plastic catheter, passed through the working channel of a flexible bronchoscope, and implanted into small airways of a single lobe using fluoro- scopic guidance. This procedure was repeated for three spherical gold markers in the opposite lung. One, 7, 14, 28, and 60 days postimplantation imaging was used to assess implant fixation. Results: Successful bronchoscopic implantation was possible for 15 of 15 transponders and 12 of 15 gold markers; 3 markers were deposited in the pleural space. Fixation at 1 day was 15 of 15 for transponders and 12 of 12 for gold markers. Fixation at 60 days was 6 of 15 for transponders and 7 of 12 for gold markers, p value = 0.45. Conclusions: Bronchoscopic implantation of both transponders and gold markers into the canine lung is feasible, but fixation rates are low. If fixation rates can be improved, implantable electromagnetic transponders may allow improved radiation therapy for lung cancer by providing real-time continuous target tracking. Developmental work is under way to improve the fixation rates and to reduce sensitivity to implantation technique. Ó 2008 Elsevier Inc. Lung cancer, Conformal radiotherapy, Bronchoscopy. INTRODUCTION Radiotherapy is a standard treatment for lung cancer, but its use has been limited by high rates of local recurrence and signifi- cant side effects (1). In the case of early stage non–small-cell lung cancer (NSCLC), recurrence and overall survival can both be improved with higher biologically damaging doses of tumor radiation (1, 2). Furthermore, by treating a small volume of tissue encompassing the tumor, radiotherapy can achieve similar survival rates and decreased complication rates when compared to larger treatment volumes (1–3). Three- dimensional conformal radiotherapy (3D-CRT) is a method of focusing radiation on the tumor, thereby increasing the dose of radiation delivered to the tumor and minimizing the volume of irradiated normal lung. It has been used successfully to deliver relatively high doses of radiation without significant increases in side effects (4). Unfortunately, lung tumor motion during respiration and daily patient setup error still limit the potential for conformal radiation therapy techniques to suc- cessfully target the tumor while reducing the irradiation of surrounding healthy lung. A method that provides real-time lung tumor localization could allow improved conformation of radiation distributions, enabling increased tumor doses and decreased irradiation to normal lung tissue. Commercially available localization tech- niques use external fiducials to correct for intrafraction tumor motion by gating the beam to coincide with a designated point in the patient’s breathing cycle or use a combination of radio- graphic snap shots to localize implanted gold fiducial markers in conjunction with real-time monitoring of external markers to monitor the patient’s breathing cycle. Accuracy, frame rate, Reprint requests to: Parag J. Parikh, M.D., Department of Radia- tion Oncology, Washington University School of Medicine, 4921 Parkview Place, Lower Level, St. Louis, MO 63110. Tel: (314) 362-8525; Fax: (314) 362-8521; E-mail: pparikh@radonc.wustl.edu M.L.M. and M.P. are consultants for Calypso Medical Technolo- gies; P.J.P., K.M.L., A.C., D.L., and J.B. receive grant support from Calypso Medical Technologies managed through Washington University; S.D. is an employee of Calypso Medical Technologies. Received Sept 17, 2007, and in revised form Dec 12, 2007. Accepted for publication Dec 13, 2007. 93 Int. J. Radiation Oncology Biol. Phys., Vol. 72, No. 1, pp. 93–98, 2008 Copyright Ó 2008 Elsevier Inc. Printed in the USA. All rights reserved 0360-3016/08/$–see front matter doi:10.1016/j.ijrobp.2007.12.055