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The Improvement of SPR Calculation with Triple Energy CT by Extracting Two Atomic Numbers of Tissue

J Zhu1*, B Liu1, X Wang1, Y Zhou2, K Nie1, R Parikh1, R Davis1, N Yue1, Y Zhang1, (1) Rutgers cancer institute of New Jersey, New Brunswick, NJ, (2) Fudan University Zhongshan Hospital, Shanghai, 31, CN,


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

This study is aimed to extract atomic numbers ( ^Z and ~Z) of tissues with triple energy CT (TECT) and to evaluate the corresponding improvement on stopping power ratio (SPR) calculation for proton therapy.

Dual-energy CT (DECT) degenerates the subtle tissue differences while assuming ^Z= ~Z=Zeff. By adding a third energy, ^Z and ~Z, presenting the atomic number in photoelectric and coherent interaction, can be differentially derived to potentially improve the CT based tissue SPR derivation. To verify this method, a virtual CT scanner was simulated in Geant4 and 3 CT image sets using 90kVp, 120kVp and 140kVp of a water phantom including 4 standard human tissues from ICRU46 were obtained. CT images were reconstructed using ifanbeam function in MATLAB. A 3D-monotonous conversion between ^Z, ~Z and mean excitation energy (Im) was generated. Another CIRS phantom with 9 inserts were simulated to obtain K series that represent the feature of CT spectra. The accuracy of SPR calculated by TECT was compared to DECT approach (90/140kVp) and single energy CT (SECT) approach (120kVp).

The comparison of SPRs showed that TECT and DECT had better performances in SPR calculation than SECT. The SPR of lung, conventionally having a larger uncertainty, showed closer values to the theoretical SPR, with less than 1% for TECT approach, comparing to 3.26% for DECT and 4.04% for SECT approaches. The accuracy of SPRs for liver and muscle from TECT was higher than those of CTs as well, with less than 2% difference from the theoretical values. However, the SPR of breast had a different trend with the higher accuracy from SECT than DECT or TECT.

The comparisons of SPRs show TECT and DECT have better performances in SPR calculation than SECT for most of tissues. However, for breast tissue, SECT performs better.

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