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A Robust Dose Calculation Algorithm Using Displacement Vector Fields From Deformable Image Registration: Simulation Study On Phantom Motion

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


(Wednesday, 7/17/2019) 9:30 AM - 10:00 AM

Room: Exhibit Hall | Forum 5

Purpose: To develop a robust algorithm that uses the displacement-vector-fields (DVF) from deformable image registration (DIR) on a voxel-by-voxel basis to perform 4D-dose optimization and calculation.

Methods: A thorax mobile phantom with three target inserts: small (10mm), medium (20mm) and large (40mm) was moved with cyclic motion patterns with varying amplitudes (0-20mm) and frequencies (0-0.5Hz. A simulation study was performed to map the CT-number values and dose distributions using the DVF that are obtained from DIR algorithms. The DVF represented voxel-by-voxel motion shifts of the tumor and surrounding organs-at-risk. A robust algorithm was developed that employed the DVF to modify the CT-number values in the CT-images and the fluence-maps of the dose distributions to perform 4D-optimization and dose calculation.

Results: The algorithm produced accurate volumes and CT-number values of the mobile targets. This algorithm provided corrections for anatomical changes and respiratory motion by remapping the CT-number values and 3D-optimized dose distributions achieving adaptive radiation therapy. The optimized dose distributions were shrunk by algorithm where they were expanded by phantom motion during dose delivery to achieve conformal 4D-dose distributions for mobile tumors. This technique required the following (a) acquisition of 4D-CT images during CT images, (b) extraction of DVF using deformable image registration during the treatment planning process (c) reproducibility of the patient breathing motion patterns between CT-simulations and dose delivery and (d) dose delivery over multiple respiratory cycles preferably intermediate or low dose rate.

Conclusion: Adaptive radiation therapy can be achieved by optimization using the voxel-by-voxel DVF induced by respiratory extracted from the 4D-CT images. This approach provides alternative approach for considering an internal target margin using 4D-CT images in the treatment planning process; and beam gating with external or internal makers during dose delivery. This robust dose optimization and calculation algorithm has potential clinical applications in adaptive radiation therapy.


Image Artifacts, Image Correlation, Dosimetry


Not Applicable / None Entered.

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