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Quantification of Intrafractional Tumor Motion in the Upper Lung Using An Electromagnetic Tumor Tracking System

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D Schmitt

D Schmitt1*, S Nill1, F Roeder1,2, F Herth3, U Oelfke1, (1) German Cancer Research Center (DKFZ), Heidelberg, Germany, (2) Heidelberg University Hospital, Heidelberg, Germany, (3) Thoraxklinik at the University of Heidelberg, Heidelberg, Germany

MO-F-WAB-12 Monday 4:30PM - 6:00PM Room: Wabash Ballroom

Purpose: To investigate the amount and variation of 3-dimensional intrafractional tumor motion in the upper lung.

Methods: We analyzed motion data for seven patients, who were enrolled by our institution in a multicenter trial evaluating investigational anchored Calypso beacons (Varian Medican Systems Inc.) in lung cancer. Beacons were placed bronchoscopically close to the tumor prior to radiotherapy. Tumors were located in a middle or upper lobe of the lung. Two patients received a hypofractionated 3D conformal irradiation and five a conventionally fractionated IMRT treatment. Average fraction time was 4.5 min and 9.8 min, respectively. In total, 162 fractions were analyzed. After patient setup using cone-beam CT, the Calypso system monitored the beacon centroid positions during all fractions with 10 Hz update rate. The centroid midline was calculated by a sliding mean of the positions in all directions with a window of 10 s, covering 2-3 breathing cycles. The midline at the time irradiation starts, called initial midline, was used as reference for intrafraction motion in general. As amplitude the average distance between each peak (inhale and exhale) and the current midline was assessed.

Results: The mean 3D distance from the initial midline over all patients was measured as (2.4+-1.3) mm. The mean of the individual patient intrafractional 3D midline drift ranges from (0.8 to 3.4) mm. Lateral, longitudinal and vertical mean amplitude was calculated to (0.9+-0.5) mm, (1.5+-1.3) mm and (1.2+-0.9) mm, respectively. Mean longitudinal motion range was up to 15 mm for 2 patients.

Conclusion: The analyzed motion data covers only tumors in the middle or upper lobes of the lung, therefore the amplitudes are biased towards smaller values. Nevertheless remarkable midline drifts could be detected. Electromagnetic tracking of lung tumor motion can provide validation of motion range assumptions from the planning 4D CT and information on midline drifts.

Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by Siemens Healthcare and Varian Medical Systems Inc.

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