Stoichiometric CT calibration of a dual energy CT for proton therapy treatment planning

• Main Author: Tan, Benjamin Keng Seng
• Other Authors: Lee Cheow Lei James
• Format: Final Year Project
• Language: English
• Published: 2018
• Subjects: DRNTU::Science
• Online Access: http://hdl.handle.net/10356/73876
• Institution: Nanyang Technological University

Background and Purpose: The range uncertainty in particle therapy should be reduced to prevent healthy tissues being damaged during radiation therapy. Here, the HU to Stopping Power Ratio (SPR) conversion range uncertainty was accessed by using different stoichiometric calibration methods to find out the best method (with the highest accuracy and least uncertainty) and the suitable phantoms for the method. Material and Methods: Three different phantoms including the CIRS 062M phantom, Gammex 467 Phantom and Catphan 504 were scanned using a Siemens SOMATOM Definition AS Computed Tomography (CT) Scanner. The CIRS 062M and Gammex 467 Phantoms had tissue substitutes plugs arranged in a configuration similar to a real patient. Three different stoichiometric CT Calibration methods were conducted to obtain the HU to SPR conversion relationship namely Schneider’s Single Energy CT (SECT) method, Zhu’s Dual energy CT (DECT) method and Bourque’s DECT method. For SECT, the phantoms were scanned in an X-ray energy of 120 kVp and for DECT the phantoms were scanned in 80 kVp and 140 kVp X-ray energy in the same configuration as SECT. After the calibration, the different calibrations were placed onto the tissues in the International Commission on Radiation Units and Measurements (ICRU) 46 and the SPR can be calculated and compared against the reference SPR from ICRU 46. The best method with the highest accuracy and least uncertainty was used to obtain the final calibration with different proton energies of 80 MeV, 150 MeV and 200 MeV to obtain the calibration table. Results: Bourque’s DECT method was found out to be the best method with the highest accuracy and the least uncertainty of 0.71% for the 140 kVp X-ray energy in proton energy of 200 MeV. CIRS 062M and Gammex 467 phantoms were suitable to be used in this method and the mean SPR values were used for the calibration table. Schneider’s SECT and Zhu’s DECT method were not as accurate as Bourque’s DECT method and only CIRS 062M phantom was found to be suitable for the two methods. Catphan was found to be unsuitable for calibration in all three different methods. The different proton energies did not show significant differences in the uncertainty in the calibration with uncertainties less than 1%. Conclusion: Bourque’s DECT method was concluded as the best method with CIRS 062M and Gammex 467 as the suitable phantoms. The X-ray energy should be 80 kVp for the lower energy and 140 kVp for the higher energy with the proton energy of 200 MeV should be used.