Analysis of the Difference in Calculation of Physical Dose for Each Patient Site of SECT and DECT Using TOPAS
E Yoon*, S Jung, J Son, B Kim, C Choi, J Kim, J Park, Seoul National University Hospital, Seoul, 11KR,
Presentations
PO-GePV-T-73 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: To calculate the carbon ion dose based on single-energy CT (SECT) and dual-energy CT (DECT) through Monte Carlo (MC) simulation, and analyze the dose calculation results by patient site.
Methods: We used TOPAS code (version 3.4) for MC simulation and modeling. For carbon ion beam scanning, a 3-D active beam scanning system was modeled. Both SECT images and DECT images were acquired with Philips IQon spectral CT which is a dual-layer detector type. 120 kVp CT images for SECT and effective atomic number (EAN) and electron density (ED) images for DECT were obtained. Then, material information for each pixel was imported into TOPAS for simulation. SECT images were imported through the stoichiometric method embedded in the code, and DECT images were imported through the in-house material converter. After dose calculation, in order to compare the dose calculation results using the two images, integral depth dose (IDD) profiles were obtained for the monoenergetic carbon ion beam irradiated from the lateral direction (case 1) and the perpendicular direction (case 2), respectively. In addition, the dose difference was analyzed after beam scanning, using the modeled beam scanning system (case 3).
Results: Before evaluating the dose calculation results for various patient sites, one site (abdomen) of the patient CT with an IRB-approved was evaluated as a preliminary result. In Cases 1 and 2, the Bragg peak position of monoenergetic ion in DECT was -1.6 / +1.7 mm from the SECT, and the dose difference at the peak was -3.8 / +3.7 % respectively. In Case 3, the dose difference for each pixel was up to 47% from the SECT at Bragg peak.
Conclusion: The difference in dose calculation for SECT and DECT image was confirmed through preliminary calculation. Dose calculations and analyzes will be performed for various patient sites.
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