• Nicholas O Roman, Wes Shepherd, Nitai Mukhopadhyay, Geoffrey D Hugo, and Elisabeth Weiss.
• Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA, USA. nroman@mcvh-vcu.edu
• Int. J. Radiat. Oncol. Biol. Phys. 2012 Aug 1; 83 (5): 1566-72.

PurposeTo evaluate implanted markers as a surrogate for tumor-based setup during image-guided lung cancer radiotherapy with audiovisual biofeedback.Methods And MaterialsSeven patients with locally advanced non-small-cell lung cancer were implanted bronchoscopically with gold coils. Markers, tumor, and a reference bony structure (vertebra) were contoured for all 10 phases of the four-dimensional respiration-correlated fan-beam computed tomography and weekly four-dimensional cone-beam computed tomography.ResultsThe systematic/random interfractional marker-to-tumor centroid displacements were 2/3, 2/2, and 3/3 mm in the x (lateral), y (anterior-posterior), and z (superior-inferior) directions, respectively. The systematic/random interfractional marker-to-bone displacements were 2/3, 2/3, and 2/3 mm in the x, y, and z directions, respectively. The systematic/random tumor-to-bone displacements were 2/3, 2/4, and 4/4 mm in the x, y, and z directions, respectively. All displacements changed significantly over time (p < 0.0001).ConclusionsAlthough marker-based image guidance may decrease the risk for geometric miss compared with bony anatomy-based positioning, the observed displacements between markers and tumor centroids indicate the need for repeated soft tissue imaging, particularly in situations with large tumor volume change and large initial marker-to-tumor centroid distance.Published by Elsevier Inc.

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