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Comparisons of Tumor Movement with Fiducial Movement Using 4D CT for Cyberknife Treatment for Lung Cancer Patients

Y Huh*1, B Yusuf2, B Holland1,3, J Jung1, AW Ju1,3, (1) East Carolina University, Greenville, NC, (2) University of North Carolina, Chapel Hill, NC, (3) Leo W. Jenkins Cancer Center, Greenville, NC


(Thursday, 8/2/2018) 7:30 AM - 9:30 AM

Room: Davidson Ballroom A

Purpose: The treatment for lung cancer using Cyberknife stereotactic body radiotherapy (SBRT) uses fiducial markers implanted in the patient’s lung surrounding the target tumor to track tumor motion during the patient’s breathing cycle. The purpose of this study is to observe how the patient’s tumor moves in comparison to the fiducials.

Methods: 18 upper lobe, 8 lower lobe, and 1 middle lobe tumors were analyzed. Within each phase of a 10-phase 4D-CT, the position of the fiducials was recorded, and the tumor contoured. The centroids of the fiducials and the tumors were compared. The root-mean-square-error (RMSE) was determined for the superior and inferior movements of the tumor centroid in comparison to the fiducial marker centroid for upper and lower lobe tumors to determine whether the proximity to the diaphragm affected tumor tracking, as well as the absolute distance differences.

Results: The mean RMSE value in the superior-inferior direction was 0.93mm and 0.81mm for the upper and lower lobe tumors respectively (p=0.794). Although the RMSE between the tumor and fiducial centroids were usually small, some cases had significant discrepancies (maximum 4.89mm). The mean absolute distance differences between the fiducial and tumor centroids for the upper and lower lobe tumors was 0.819mm and 0.391mm respectively.

Conclusion: Patients with upper lobe tumors collectively had more spread out RMSE values in comparison to the patients with lower lung tumors due to a handful of cases with outlier RMSE values. The absolute distance difference showed similar results. The general clinical consensus among physicians that upper lobe tumors are tracked better may not be applicable to all patients, and may result in marginal misses. Future research can potentially decrease the uncertainty of fiducial marker tracking. Correlation of this data with the real-time fiducial tracking data on the CyberKnife Synchrony system used during patient treatment is needed.


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