Proton stopping power determination with dual-energy CT in 3D-printed tissue/air cavity surrogates

Published

July 1, 2019

Author(s)

Jerimy Polf, Matthew Mille, Sina Mossahebi, Haijian Chen, Paul Maggi, Heather H. Chen-Mayer

Abstract

Purpose: To study the accuracy with which proton stopping power ratio (SPR) can be determined with dual-energy computed tomography (DECT) for small structures and bone-tissue-air interfaces like those found in the head or in the neck. Methods: Hollow cylindrical polylactic acid (PLA) plugs (3 cm diameter, 5 cm height) were 3D- printed containing either one or three septa with thicknesses tsepta = 0.8 mm, 1.6 mm, 3.2 mm and 6.4 mm running along the length of plug. The cylinders were inserted individually into a tissue equivalent head phantom (16 cm diameter, 5 cm height). First, DECT scans were obtained using a Siemens SOMATON Definition Edge CT scanner. Effective atomic number (Zeff) and electron density (e) images were reconstructed from the DECT to produce SPR-CT images of each plug. Second, independent elemental composition analysis of the PLA plastic was used to determine the Zeff and e for calculating the theoretical SPR (SPR-TH) using the Bethe-Bloch equation. Finally, for each plug, a direct measurement of SPR (SPR-DM) was obtained in a clinical proton beam. The values of SPR-CT, SPR-TH, and SPR-DM were compared. Results: SPR-CT for PLA agreed with SPR-TH when tsepta ≥ 3 mm (for CT slice thicknesses of 0.5 mm, 1.0 mm, and 3.0 mm). The density of PLA was found to decrease with thickness when tsepta < 3 mm. As tsepta (and density) decreased, the SPR-CT values also decreased, in good agreement with the behavior of SPR-DM. Conclusion: The DECT-based method for calculating SPR in thin heterogeneities showed good agreement with both theoretical and directly measured SPR values. The DECT scans accurately predicted the reduction in SPR associated with decreasing density as the septa thicknesses decreased.

Citation

Medical Physics

Pub Type

Journals

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Keywords

proton stopping ratio, proton beam therapy, DECT, 3D printed tissue phantom

Citation

Polf, J. , Mille, M. , Mossahebi, S. , Chen, H. , Maggi, P. and Chen-Mayer, H. (2019), Proton stopping power determination with dual-energy CT in 3D-printed tissue/air cavity surrogates, Medical Physics, [online], https://doi.org/10.1002/mp.13587 (Accessed October 25, 2024)