A stoichiometric calibration method for dual energy computed tomography

Area of Science:

• Medical Physics
• Radiotherapy
• Imaging Science

Background:

• Accurate radiotherapy dose calculation requires precise patient tissue composition data.
• Traditional CT calibration methods are effective for single-energy CT but less so for dual-energy CT (DECT).
• DECT offers potential for improved tissue characterization without calibration curves.

Purpose of the Study:

• To adapt the stoichiometric calibration method for DECT to accurately determine electron density (ED) and effective atomic number (EAN).
• To validate the adapted method using theoretical models and phantom measurements.
• To assess the impact of DECT-derived tissue data on ion beam therapy dose calculations.

Main Methods:

• Revised stoichiometric calibration method applied to DECT data.
• Utilized ICRP human tissue compositions and XCOM database for theoretical validation.
• Phantom measurements performed on a Siemens SOMATOM Definition Flash DECT scanner.
• Calculated ion stopping powers and range uncertainties for therapeutic proton, helium, and carbon ions.

Main Results:

• DECT stoichiometric calibration achieved Hounsfield Unit (HU) predictions within ±1.3 HU of theoretical values.
• Mean absolute errors for ED and EAN were (0.3 ± 0.4)% and (1.6 ± 2.0)%, respectively.
• Mean absolute errors for proton stopping powers and I-values were (0.5 ± 0.4)% and (4.1 ± 2.7)%, respectively.
• Uncertainties in ion ranges were below 1.3 mm for protons and 0.5 mm for carbon ions.

Conclusions:

• The adapted stoichiometric calibration method provides highly accurate tissue characterization using DECT.
• This method enhances accuracy for ion beam therapy and potentially photon beam therapy.
• The approach minimizes the need for spectrum measurements or empirical corrections.