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Quantitative Assessment of 4D Cone-Beam CT Based Image Guidance for Patient Positioning in Precision Radiotherapy

A Gopal

A Gopal*, S Lee, K Mittauer, D Kahler, B Lu, S Samant, Univ. of Florida, Gainesville, FL

SU-C-213CD-6 Sunday 1:30:00 PM - 2:15:00 PM Room: 213CD

Purpose: To evaluate the precision of 4D cone-beam CT as an image guidance tool for stereotactic body radiotherapy using intensity modulated arc or fixed gantry radiotherapy in sites with significant intrafraction tumor motion
Methods: 4D cone-beam CT (4D-CBCT) is a recent innovation that has the potential to significantly improve the precision of highly conformal radiotherapy treatments. The performance of a commercial Elekta Synergy X-ray Volume Imager (XVI) 4D-CBCT system was quantitatively analyzed using a motor driven respiration phantom for a series of uniform and irregular breathing patterns. The quality of image guidance was assessed based on the precision of the 4D-CBCT registration obtained from the XVI system with respect to the known motion of the respiration phantom (Quasar ModusQA). The quality of the registration was evaluated with various scan acquisition settings for field size, projection arc, gantry speed, etc., to develop an optimized image guidance protocol for 4D treatment sites.
Results: The results indicated that the 4D-CBCT registration shifts were in good overall agreement with the actual phantom motion. After rigid registration corrections using static regions of the phantom to eliminate systematic shifts, the respiration amplitudes were accurately reflected to within 1-3 mm for most breathing patterns, which is well within the expected uncertainty of registration algorithms as well as the amplitude and phase variability of the motor control. However, position differences in individual phase comparisons were found to be as high as 8-10 mm. We also observed that the larger field settings (m²0) for the 4D-CBCT acquisition rendered comparable accuracy to smaller vendor recommended fields (S20).
Conclusions: The accuracy of 4D-CBCT based patient positioning for treatment sites with significant respiratory motion was verified along with its potential to facilitate greater precision for dose convergence in hyperfractionated radiotherapy as well as to evaluate the feasibility of respiration gated radiotherapy.

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