CLINICAL INVESTIGATION Lung HIGH RETENTION AND SAFETY OF PERCUTANEOUSLY IMPLANTED ENDOVASCULAR EMBOLIZATION COILS AS FIDUCIAL MARKERS FOR IMAGE-GUIDED STEREOTACTIC ABLATIVE RADIOTHERAPY OF PULMONARY TUMORS JULIAN C. HONG, M.S.,* YAO YU, B.S.,* AARTI K. RAO, B.S.,* SONJA DIETERICH,PH.D.,* PETER G. MAXIM,PH.D.,* QUYNH-THU LE, M.D.,* MAXIMILIAN DIEHN, M.D., PH.D.,* DANIEL Y. SZE, M.D., PH.D., y NISHITA KOTHARY, M.D., y AND BILLY W. LOO,JR., M.D., PH.D.* *Department of Radiation Oncology, Stanford University, Stanford, California, and y Department of Radiology, Stanford University, Stanford, California Purpose: To compare the retention rates of two types of implanted fiducial markers for stereotactic ablative radio- therapy (SABR) of pulmonary tumors, smooth cylindrical gold ‘‘seed’’ markers (‘‘seeds’’) and platinum endovas- cular embolization coils (‘‘coils’’), and to compare the complication rates associated with the respective implantation procedures. Methods and Materials: We retrospectively analyzed the retention of percutaneously implanted markers in 54 con- secutive patients between January 2004 and June 2009. A total of 270 markers (129 seeds, 141 coils) were implanted in or around 60 pulmonary tumors over 59 procedures. Markers were implanted using a percutaneous approach under computed tomography (CT) guidance. Postimplantation and follow-up imaging studies were analyzed to score marker retention relative to the number of markers implanted. Markers remaining near the tumor were scored as retained. Markers in a distant location (e.g., pleural space) were scored as lost. CT imaging artifacts near markers were quantified on radiation therapy planning scans. Results: Immediately after implantation, 140 of 141 coils (99.3%) were retained, compared to 110 of 129 seeds (85.3%); the difference was highly significant (p < 0.0001). Of the total number of lost markers, 45% were reported lost during implantation, but 55% were lost immediately afterwards. No additional markers were lost on longer- term follow-up. Implanted lesions were peripherally located for both seeds (mean distance, 0.33 cm from pleural surface) and coils (0.34 cm) (p = 0.96). Incidences of all pneumothorax (including asymptomatic) and pneumotho- rax requiring chest tube placement were lower in implantation of coils (23% and 3%, respectively) vs. seeds (54% and 29%, respectively; p = 0.02 and 0.01). The degree of CT artifact was similar between marker types. Conclusions: Retention of CT-guided percutaneously implanted coils is significantly better than that of seed markers. Furthermore, implanting coils is at least as safe as implanting seeds. Using coils should permit implan- tation of fewer markers and require fewer repeat implantation procedures owing to lost markers. Ó 2011 Elsev- ier Inc. Implanted fiducial markers, Image-guided radiation therapy (IGRT), Stereotactic ablative radiotherapy (SABR), Stereotactic body radiotherapy (SBRT), Endovascular embolization coils, Gold seed fiducial markers. INTRODUCTION One of the most important emerging developments in radia- tion therapy for small, malignant lung tumors is stereotactic ablative radiotherapy (SABR), also known as stereotactic body radiation therapy (SBRT), in which very precise and ac- curate delivery of highly conformal and dose-intensive radi- ation can produce a high rate of tumor ablation while sparing the surrounding normal tissues. Image-guided radiation ther- apy (IGRT) is an important component of such treatments, since, unlike tumors in the brain that have a fixed relationship to skeletal anatomy, pulmonary tumors can be highly mobile. A challenge of IGRT of soft tissue targets is the lack of con- trast when using planar imaging. Volumetric computerized tomography (CT)-based imaging integrated into the treat- ment system can provide precise three-dimensional Reprint requests to: Billy W. Loo, Jr., M.D., Ph.D., Department of Radiation Oncology, Stanford University and Cancer Center, 875 Blake Wilbur Drive, Stanford, CA 94305-5847. Tel: (650) 736- 7143; Fax: (650) 725-8231; E-mail: BWLoo@Stanford.edu; or Nishita Kothary, M.D., Department of Radiology, Stanford Uni- versity, 300 Pasteur Drive, H3652, Stanford, CA 94305-5642; Tel: (650) 498-6020; Fax: (650) 725-0533; E-mail: kothary@ stanford.edu. Conflict of interest: B.L. has received speaking honoraria from Accuray, Inc. and Varian Medical Systems. Received Feb 13, 2010, and in revised form April 6, 2010. Accepted for publication April 23, 2010. 85 Int. J. Radiation Oncology Biol. Phys., Vol. 81, No. 1, pp. 85–90, 2011 Copyright Ó 2011 Elsevier Inc. Printed in the USA. All rights reserved 0360-3016/$–see front matter doi:10.1016/j.ijrobp.2010.04.037