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Four-Dimensional Dose Calculation Algorithm Using Displacement Vector Fields From Deformable Image Registration for Proton Therapy as An Alternative to Robust Planning

I Ali1*, N Alsbou2, S Ahmad1, (1) University of Oklahoma Health Sciences Center, Oklahoma City, OK, (2) Department of Engineering and Physics, University of Central Oklahoma, Edmond, OK,

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To develop an algorithm with 4D-dose optimization and dose calculation that can be used for adaptive proton therapy as an alternative technique for robust treatment planning using displacement-vector fields (DVF) obtained from deformable-image-registration.
Methods: Helical, axial and cone-beam CT-image of a mobile thorax phantom that moved with controlled cyclic motion patterns with amplitudes ranging 0-30mm and frequencies 0-0.5Hz. The phantom included three soft-tissue-equivalent target that simulate lesions with different sizes ranging 10-40mm inserted in low-density foam that mimic lung-tissue. The CT-images of the mobile phantom were registered to static CT-images and DVF were extracted using different motion patterns. The DVF were employed to calculate the shifts on a voxel-by-voxel based for the whole phantom. An algorithm was developed which used the DVF to reproduce the static CT-number values in the mobile CT-images and regenerate the fluence map to perform 4D-optimization and dose calculation.
Results: The produced CT-number values by remapping the CT-images with deformable-image-registration corrected for anatomical variations and respiratory motion. The volumes for the mobile targets which were elongated in the motion direction were corrected with DVF. The maximal and minimal DVF correlated linearly with motion amplitude of the mobile targets which was used to extract the shifts of the different voxels particularly in the mobile targets embedded in lung phantom. This 4D-dose calculation algorithm employed DVF extracted from deformable image registration to obtain conformal 4D-dose distribution considering phantom motion. The dose distributions were shrunk by optimization which in turn were expanded by phantom motion to produce conformal 4D-dose distributions.
Conclusion: This algorithm provides 4D-optimized dose calculation which used DVF from deformable image registration to correct for the mobile target volumes and CT-number variations due to motion artifacts. This approach represented an alternative for robust treatment planning in proton therapy using static margins and management of patient motion.

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