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In Silico Modeling for the Dosimeteric Effect of Metallic Shields On Artifact-Free CT Images Produced by Dummy Shields

J Park

J Park1*, J Lee1 , H Kim2 , C Choi3 , I Kim2,3,4 , S Lee1 , S Ye1,2 , (1) Department of Transdisciplinary Studies, Program in Biomedical Radiation Sciences, Seoul National University Graduate School of Convergence Science, (2) Interdisciplinary Program in Radiation Applied Life Science, Seoul National University College of Medicine, Seoul, Korea.(3) Seoul National University Hospital, Seoul, (4) College of Medicine, Seoul National University


TU-L-GePD-T-3 (Tuesday, August 1, 2017) 1:15 PM - 1:45 PM Room: Therapy ePoster Lounge

Purpose: To evaluate the dosimetric effect of metallic shields on artifact-free CT images produced by dummy shields.

Methods: Three patients were selected to place a dummy shield on their lips and eye. A 3D scanner was used to extract the shapes and dimensions of metallic shields, and these scanned data were transferred into a 3D printer. A dummy shield was then produced using bio-resin materials and used to produce artifact-free CT images in the patient. Treatment plans were designed using the Eclipse TPS with electron Monte Carlo algorithm (eMC) for dose calculation. EGS/BEAMnrc and EGS/DOSXYZnrc were commissioned from our measurement data of Varian 21EX for 6, 9 and 12 MeV beams. The CT images were converted into a phantom through the ctcreate program. For comparison of eMC and EGS-based MC, two CT phantoms were generated by assigning the maximum allowable CT number (3071) to the shield region for eMC and by assigning real mass densities and materials of the metallic shields for EGS-based MC. The calculated doses were transferred to CERR with RT structure files.

Results: For an eye shield case, the MC doses on the right lens were less than 20% of prescription dose, while the corresponding eMC calculated doses were unrealistic values of approximately 50% of prescription dose. For two lip cases, eMC results also showed unrealistic doses of approximately 80%-90% behind the shield, while the MC results were more realistic doses of approximately 20%-40% behind the shield.

Conclusion: A dummy shield for electron radiation therapy can be easily produced and implemented into the patients utilizing a 3D scanner and a 3D printer. The artifact-free CT images were successfully incorporated into the CT-based Monte Carlo simulations. The developed method can predict the realistic dose distributions around a metallic shield.

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