Program Information
Validating a Fiducial-Less Tracking Method for Radiation Therapy of Abdominal Tumors by Diaphragm Disparity Analysis
D Dick1*, X Wu2 , W Zhao1 , (1) University of Miami,Miami, FL, (2) Biophysics Research Institute of America, North Miami Beach, Florida
Presentations
TU-C1-GePD-J(A)-6 (Tuesday, August 1, 2017) 9:30 AM - 10:00 AM Room: Joint Imaging-Therapy ePoster Lounge - A
Purpose: To investigate the feasibility of localizing abdominal tumor through tracking lung-diaphragm border and validation by gold fiducial markers
Methods: In this simulation study, an abdominal 4DCT dataset acquired previously, containing 20 phases of the breathing cycle, was used as the testing data. One set of DRR images (45 degrees) was generated for each phase. Five specified anatomical points along the lung-diaphragm interface on each of the DRR images were identified by cross-correlation. The fiducial marker was identified for each phase of the breathing cycle by using 3D convolution to generate the gravity center serving as the measured center of the fiducial. A linear model was created to correlate the diaphragm’s disparity of the five identified anatomical points with the corresponding position of the fiducial. To reduce measurement errors, phases with error above 2-standard deviations of all errors from the model were voided. The linear model was then refined. To verify the established linear model, we used the leave-one-out cross validation methodology for each phase of the breathing cycle then compared the calculated fiducial’s position and the measured fiducial position.
Results: The maximum difference between the calculated and the measured position values across the 20 phases were 0.7, 0.3 and 3.1 mm (3mm between CT slices) in the x, y and z directions respectively, which yielded a maximum squared-error value of 2.0mm. The outcomes of the verification process, by eliminating each phase, produced a maximum squared-error of 2.5mm.
Conclusion: Gold fiducial markers, requiring surgical procedure to be deployed, are conventionally used in radiation therapy. This study showed that the diaphragm and fiducial position are closely related. The developed diaphragm disparity analysis approach, verified with clinically accepted errors, has the potential to replace fiducial markers for clinical application. The tracking method will be further investigated in a larger cohort of patients.
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