The potential of dual-energy CT to reduce proton beam range uncertainties

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The potential of dual-energy CT to reduce proton beam range uncertainties

Bar, E; Lalonde, A; Royle, G; Lu, H-M; Bouchard, H; (2017) The potential of dual-energy CT to reduce proton beam range uncertainties. Medical Physics , 44 (6) pp. 2332-2344. 10.1002/mp.12215. Green open access

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Abstract

PURPOSE: Dual‐energy CT (DECT) promises improvements in estimating stopping power ratios (SPRs) for proton therapy treatment planning. Although several comparable mathematical formalisms have been proposed in literature, the optimal techniques to characterize human tissue SPRs with DECT in a clinical environment are not fully established. The aim of this work is to compare the most robust DECT methods against conventional single‐energy CT (SECT) in conditions reproducing a clinical environment, where CT artifacts and noise play a major role on the accuracy of these techniques.METHODS: Available DECT tissue characterization methods are investigated and their ability to predict SPRs is compared in three contexts: (a) a theoretical environment using the XCOM cross section database; (b) experimental data using a dual‐source CT scanner on a calibration phantom; (c) simulations of a virtual humanoid phantom with the ImaSim software. The latter comparison accounts for uncertainties caused by CT artifacts and noise, but leaves aside other sources of uncertainties such as CT grid size and the I‐values. To evaluate the clinical impact, a beam range calculation model is used to predict errors from the probability distribution functions determined with ImaSim simulations. Range errors caused by SPR errors in soft tissues and bones are investigated. RESULTS: Range error estimations demonstrate that DECT has the potential of reducing proton beam range uncertainties by 0.4% in soft tissues using low noise levels of 12 and 8 HU in DECT, corresponding to 7 HU in SECT. For range uncertainties caused by the transport of protons through bones, the reduction in range uncertainties for the same levels of noise is found to be up to 0.6 to 1.1 mm for bone thicknesses ranging from 1 to 5 cm, respectively. We also show that for double the amount noise, i.e., 14 HU in SECT and 24 and 16 HU for DECT, the advantages of DECT in soft tissues are lost over SECT. In bones however, the reduction in range uncertainties is found to be between 0.5 and 0.9 mm for bone thicknesses ranging from 1 to 5 cm, respectively. CONCLUSION: DECT has a clear potential to improve proton beam range predictions over SECT in proton therapy. However, in the current state high levels of noise remain problematic for DECT characterization methods and do not allow getting the full benefits of this technology. Future work should focus on adapting DECT methods to noise and investigate methods based on raw‐data to reduce CT artifacts.

Type:	Article
Title:	The potential of dual-energy CT to reduce proton beam range uncertainties
Open access status:	An open access version is available from UCL Discovery
DOI:	10.1002/mp.12215
Publisher version:	http://dx.doi.org/10.1002/mp.12215
Language:	English
Additional information:	This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords:	Science & Technology, Life Sciences & Biomedicine, Radiology, Nuclear Medicine & Medical Imaging, dual-energy CT, proton stopping power, proton therapy, range uncertainties, tissue characterization, MONTE-CARLO SIMULATIONS, STOPPING-POWER, STOICHIOMETRIC CALIBRATION, EXPERIMENTAL-VERIFICATION, ATTENUATION COEFFICIENTS, COMPUTED-TOMOGRAPHY, TISSUE PARAMETERS, ATOMIC NUMBERS, DENSITY, SINGLE
UCL classification:	UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Med Phys and Biomedical Eng
URI:	https://discovery.ucl.ac.uk/id/eprint/10055343