4D-CT Prediction of Inter- and Intrafraction Lung Tumor Motion During Fractionated Stereotactic Body Radiation Therapy
A Rashid1*, Y Niu2, D Pang3, (1) Medstar Georgetown University Hospital, Washington, DC, (2) Medstar Georgetown University Hospital, Washington, DC, (3) Georgetown University Hospital, Washington, DC
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PO-GePV-T-364 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: Respiratory-induced lung tumor motion is regularly assessed by utilizing a single four-dimensional computed tomography (4D-CT) pre-treatment scan in order to account for tumor motion during delivery of stereotactic body radiation therapy (SBRT).
Methods: All patients underwent free breathing planning 4D-CT scans in preparation for robotic fiducial-based fractionated SBRT in either 3 or 5 treatments. Fiducial motion was assessed on each phase of the 4D-CT scans by measuring the fiducial centroid displacements in the anterior-posterior (AP), superior-inferior (SI), and left-right (LR) directions. Intrafraction centroid motion during SBRT delivery was extracted from the SBRT delivery system and analyzed using custom MATLAB software. Real-time tumor motion was then compared to predicative tumor motion based on pre-treatment 4D-CT scans by assessing three-dimensional fiducial centroid translations.
Results: A total of 21 SBRT fractions were delivered to lung tumors. As expected, cohort-averaged 4D-CT fiducial displacements were largest in the SI direction followed by the AP and LR directions. Cohort-averaged mean fiducial displacements based upon 4D-CT and real-time tracking were measured to be 2.67 ± 3.83 mm versus 3.02 ± 0.20 mm (p = 0.68), 0.51 ± 0.50 mm versus 1.74 ± 0.34 mm (p < 0.0001), and 0.47 ± 0.51 mm versus 0.57 ± 0.12 mm (p = 0.39) in the SI, AP, and LR directions, respectively. Cohort-averaged maximal fiducial displacements based upon 4D-CT and real-time tracking were measured to be 4.12 ± 4.62 mm versus 14.35 ± 3.018 mm (p < 0.0001), 1.15 ± 0.51 mm versus 4.91 ± 1.74 mm (p< 0.0001), and 0.99 ± 0.74 mm versus 2.99 ± 0.57 mm (p < 0.0001) in the SI, AP, and LR directions, respectively.
Conclusion: A single planning 4D-CT scan is unlikely to capture all observable tumor motion that can manifest during a given SBRT treatment fraction, particularly in the SI and AP dimensions.
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