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Accumulated Dose Estimation in Lung Stereotactic Body Radiation Therapy Using Deformable Image Registration Algorithm
Q Wu*, c liu , s devpura , m ajlouni , B Movsas , I Chetty , Henry Ford Health System, Detroit, MI
Presentations
WE-RAM3-GePD-J(A)-4 (Wednesday, August 2, 2017) 10:30 AM - 11:00 AM Room: Joint Imaging-Therapy ePoster Lounge - A
Purpose: To estimate accumulated dose to targets and OARs for lung cancer patients treated with SBRT.
Methods: CBCT and planning CT (pCT) image datasets for lung cancer patients treated with SBRT (12Gyx4), were deformably registered. ITV-PTV margin was uniformly 5 mm. The pCT was deformed and resampled based on the displacement vector field (DVF) from the pCT/CBCT registration, so as to minimize HU issues associated with CBCT. Deformable image registration (DIR) was based on a multi-resolution b-spline algorithm with mutual-information as the similarity metric. Dose-of-the-day was calculated on the deformed pCT datasets, for each of the four fractions, and dose was accumulated using an energy-mass-mapping algorithm.
Results: Mean (standard deviation) of cumulative mean dose minus plan mean dose was -0.6% (1.2%) for the GTV, -0.9% (1.3%) for the PTV, -1.8% (1.2%) for the spinal cord, and -1.6% (4.1%) for total lung-PTV. Mean (standard deviation) of cumulative D95 minus plan D95 was -0.5% (1.3%) for the GTV and -2.9% (2.6%) for the PTV. Mean (standard deviation) of cumulative max. dose minus plan max. dose was -1.1% (1.0%) for the GTV, -1.1% (0.9%) for the PTV, 3.4% (11.7%) for the spinal cord, and 1.1% (2.0%) for total lung-PTV. Mean (standard deviation) of cumulative min. dose minus plan min. dose was 2.1% (3.5%) for the GTV and -14.2% (5.9%) for the PTV.
Conclusion: Cumulative doses using deformable dose accumulation were found to be less than planned doses. The planned dose degradation is noted in the DVH shoulders, where min. differences >10% are observed for the PTV, albeit with the GTV min. dose maintained within (2-4%). OAR max. doses for critical structures such as the spinal cord are shown to increase >10%, which is an important consideration for this serial organ, in the context of SBRT lung treatment.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by a grant from Varian Medical Systems, Palo Alto, CA
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