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Dosimetric Evaluation of 4D-CBCT Reconstructed by Simultaneous Motion Estimation and Image Reconstruction (SMEIR) for Carbon Ion Therapy of Lung Cancer

D Shrestha*, N Qin , Y Zhang , M Tsai , X Jia , J Wang , UT Southwestern Medical Center, Dallas, TX


(Wednesday, 8/1/2018) 10:30 AM - 11:00 AM

Room: Exhibit Hall | Forum 2

Purpose: Motion management is critical for the efficacy of carbon ion radiation therapy for moving targets such as lung tumors. The purpose of this work is to evaluate the feasibility of using 4D-CBCT reconstructed by SMEIR for dose reconstruction and accumulation in carbon ion treatment of lung cancer.

Methods: Motion compensated 4D-CBCT was reconstructed by the SMEIR algorithm to capture the most updated anatomy with an updated inter-phase motion model on the treatment day. Projections of all the phases of CBCT were simulated from the planning 4D-CT by a ray tracing technique. Treatment planning and dose calculation were performed with a GPU based Monte Carlo dose calculation software for carbon ion therapy. Optimization of the treatment plan was performed on the average CT to obtain the optimal intensity of the carbon ions. From the optimized plan, dose distributions on individual phase of 4D-CT and 4D-CBCT were calculated by the Monte Carlo based dose engine. Dose accumulation was performed on 4D-CBCT images using deformable vector fields (DVF) generated by SMEIR. The accumulated dose of PTV based on 4D-CBCT was then compared to the accumulated dose calculated on 4D-CT, where DVFs between different phases was obtained by the demons deformable registration algorithm. Dose value histograms (DVH), absolute deviations for the planning target volume (PTV) between the two sets of plans were quantitatively evaluated for the minimal dose (∆D_95) and the 100% prescription dose coverage (∆V_(100%)).

Results: Excellent agreement was found between the 4D-CT and 4D-CBCT based PTV-DVH curves. The values of average (∆D_95) and (∆V_(100%)) calculated between the 4D-CT and 4D-CBCT based plans were 5.72% and 1.73% respectively for the two patient case studies.

Conclusion: SMEIR reconstructed 4D-CBCTs can potentially be used for motion estimation, dose evaluation and adaptive treatment planning for lung cancer carbon ion therapy.


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