(Monday, 7/30/2018) 3:45 PM - 4:15 PM
Room: Exhibit Hall | Forum 5
Purpose: To develop a four-dimensional (4D) dose optimization and calculation algorithm on 4D-CT-number maps with tissue heterogeneity using displacement-vector-fields (DVF) from different deformable-image-registration algorithms (DIR) in order to consider for anatomical variations and respiratory motion to achieve adaptive radiation therapy.
Methods: A simulation study was performed to remap CT-number values and dose distributions using DVF obtained from DIR algorithms. The DVF represent a voxel-by-voxel motion of the tumor and surrounding organs-at-risk in the region of interest. These DVF were employed to modify the intensity maps from 3D-conformal and intensity-modulation optimized plans to perform 4D optimization on remapped CT-numbers to account for heterogeneity to consider anatomical variation and respiratory motion.
Results: This dose calculation algorithm produces 4D-optimized plans from the stationary 3D-confromal or intensity-modulated plans using DVF’s extracted from DIR algorithms. It performs optimization by shrinking and remapping the dose distribution that are obtained from dose optimization on stationary images. The unfolding of the 4D-dose distributions as the patient move during dose delivery will produce an equivalent dose distribution that is optimize in 3D for the stationary target and organs at risk. Heterogeneity correction is also considered by remapping the CT-number values in the CT images using the DVF’s in order to reverse motion artifacts. The advantages of this approach include achieving equivalent conformal doses without any restriction on anatomical variations and patient breathing during dose delivery. The limitations of this technique include (a) requirement of to perform 4D-CT imaging with different motion phases and accurate quantification of patient motion and (b) reproducibility of the DVF by the different DIR algorithms.
Conclusion: This algorithm provides a novel approach to perform adaptive radiation therapy using 4D-dose optimization and calculation with heterogeneity correction using remapped CT numbers which is a practical and convenient alternative to manage respiratory motion of cancer patients.
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