Advances in radiation therapy permit high-dose, 3D-focused irradiation to lung tumors. This may improve tumor eradication and reduce normal tissue damage. Tumor motion due to respiration remains a significant problem. The accuracy of breathing gating techniques that depend on abdominal or chest wall motion as surrogates for lung tumor motion have not been well defined. We studied the feasibility of implantating gold markers bronchoscopically in and around lung tumors and evaluated its usefulness for estimating tumor motion during gated radiotherapy.
Patients with lung tumor motion greater than 1cm were recruited. Sterile, gold fiducials (ACCULOC®, NMPE) with a diameter of 1.0 –2.0 mm were implanted in a tetrahedral spread around primary lung tumors in 3 patients. Each fiducial was loaded at the tip of a plastic catheter with an inner wire to serve as a releasing plunger. Up to 5 fiducials per patient were placed under fluoroscopic guidance. Respiratory gating dependent on abdominal displacement was used during radiation (RPM, Varian Medical Systems).Images were also captured continuously during the gated treatment to determine fiducials’ motion and location relative to the treatment field.
No complications occurred during bronchoscopic implantation of fiducials. Each procedure lasted approximately 15 minutes. In patient #1, three of the five fiducials migrated to the stomach leaving only two for daily imaging. Fiducial #1 was located directly in the tumor and fiducial #2 was located between the posterior chest wall and the tumor. Table 1 displays mean(SD) and maximum fiducial excursions for left-right(LR),superior-inferior (SI),and anterior-posterior(AP)directions as measured on portal images.
Bronchoscopic placement of fiducials in and around lung tumors is safe and useful for detecting lung tumor motion. Detection of tumor motion by externally acquired respiratory trace may not be sufficiently accurate for reducing the field margin and may result in inadequate tumor coverage during treatment.
The use of bronchoscopically-implanted lung fiducials is a promising aid to improving accuracy, better target coverage, and spare more healthy tissue during 3D-conformal radiotherapy for moving tumors.
Rodolfo Morice, Product/procedure echnique that is considered research and is NOT yet approved for any purpose. Technique used for implantation of fiducials in the lung is experimental. This protocol was approved by our institutional IRB.