Program Information
Dose Deviation Due to the Combination Effect of MRI Geometric Distortion and Local Dose Gradient in MRI-Based IMRT Planning
Y Yan*, J Yang , G Ibbott , J Wang , MD Anderson Cancer Center, Houston, TX
Presentations
SU-K-601-11 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 601
Purpose: To explore the inter-dependence of dose deviation on MRI geometric distortion and local dose gradient for MRI-based intensity modulated radiation therapy (IMRT) planning.
Methods: Residual geometric distortion of a 1.5T MRI system was measured and a distortion model was developed to simulate the residual MRI geometric distortion. This distortion model was applied to the clinical computed tomography (CT) image for 14 patients and dose was recalculated based on the distorted CT image. The dosimetric difference between the distorted plan and the original clinical plan was calculated at voxel level and correlated with the local dose gradient in the original clinical plan. A third order polynomial function was used to describe the dependence of the dose deviation of the distorted plan on MRI geometric distortion and local dose gradient. We set the acceptable absolute dose deviation to be 3 Gy. The distortion was stratified to 4 levels from 2 mm to 10 mm with a 2 mm increment and local dose gradient from 0-2 Gy/mm with a 0.5 Gy/mm increment.
Results: More pronounced dose deviation was observed when the geometric distortion or the local dose gradient was increased. With a fixed geometric distortion, the threshold of acceptable dose gradient were 2.45, 2.17, 1.66, and 1.04 Gy/mm for the 4 distortion levels, respectively. With a fixed local dose gradient, the threshold of acceptable geometric distortion were 9.59, 7.30, and 6.79 mm for gradient levels greater than 0.5 Gy/mm.
Conclusion: We assessed the inter-dependence of the absolute dose deviation due to MRI geometric distortions and local dose gradients. The data obtained from this study may be used in clinic to estimate the dose deviation due to the geometric distortion in MRI-based treatment planning.
Funding Support, Disclosures, and Conflict of Interest: Dr. Jihong Wang received funding support from Elekta and General Electric.
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