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Determination of proton stopping power ratio with dual‐energy CT in 3D‐printed tissue/air cavity surrogates
Author(s) -
Polf Jerimy C.,
Mille Matthew M.,
Mossahebi Sina,
Chen Haijian,
Maggi Paul,
ChenMayer Huaiyu
Publication year - 2019
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.13587
Subject(s) - materials science , scanner , digital enhanced cordless telecommunications , nuclear medicine , imaging phantom , stopping power , effective atomic number , hounsfield scale , biomedical engineering , computed tomography , optics , medicine , physics , attenuation , radiology , telecommunications , detector , computer science , wireless
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 t septa = 0.8, 1.6, 3.2, and 6.4 mm running along the length of the 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 SOMATOM Definition Edge CT scanner. Effective atomic number ( Z eff ) and electron density ( ρ 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 Z eff and ρ 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 The SPR‐CT for PLA agreed with SPR‐DM for t septa ≥ 3 mm (for CT slice thicknesses of 0.5, 1.0, and 3.0 mm). The density of PLA was found to decrease with thickness when t septa < 3 mm. As t septa (and density) decreased, the SPR‐CT values also decreased, in good agreement with SPR‐DM and SPR‐TH. Conclusion Overall, the DECT‐based SPR‐CT was within 3% of SPR‐TH and SPR‐DM in the high‐density gradient regions of the 3D‐printed plugs for septa greater than ~ 3mm in thickness.