The potential of dual-energy computed tomography for quantitative decomposition of soft tissues to water, protein and lipid in brachytherapy

Abstract

Abstract. Dosimetric accuracy of radiation treatment planning in brachytherapy depends on knowledge of tissue composition. It has been speculated that soft tissues can be decomposed to water, lipid and protein. The aim of our work is to evaluate the accuracy of such tissue decomposition. Selected abdominal soft tissues, whose average elemental compositions were taken from literature, were decomposed using dual energy computed tomography to water, lipid, and protein via the three-material decomposition method. The quality of the decomposition was assessed using relative differences between the (i) mass energy absorption and (ii) mass energy attenuation coefficients of the analyzed and approximated tissues. It was found that the relative differences were less than 2% for photon energies larger than 10 keV. The differences were notably smaller than the ones for water as the transport and dose scoring medium. The choice of the water, protein and lipid triplet resulted in negative elemental mass fractions for some analyzed tissues. As negative elemental mass fractions cannot be used in general purpose particle transport computer codes using the Monte Carlo method, other triplets should be used for the decomposition. These triplets may further improve the accuracy of the approximation as the differences were mainly caused by the lack of high-Z materials in the water, protein and lipid triplet.

Patient Dose Computation

“…As most tissues consist of up to ten elements, direct algebraic decomposition is not possible even with two tube voltages, so still approximations are used. Most efforts with dual energy CT have been for brachytherapy with low-energy photons that is more sensitive to composition differences than high-energy photons (Landry et al, 2011;Malusek et al, 2013) and for range verification of light ion beam therapy (Landry et al, 2013).…”

A model-based iterative reconstruction algorithm DIRA using patient-specific tissue classification via DECT for improved quantitative CT in dose planning

“…In the two‐material decomposition method (2MD) in DECT, the summation rule (1) and the normalization condition w 1 + w 2 = 1 lead to a system of equations that can be written in the matrix form aswhere the mass fractions w 1 and w 2 and the mass density ρ of the mixture are unknown, the linear attenuation coefficients and of the mixture are known. Eq.…”

“…The method was also applied for the determination of (a) iron content in liver composed of soft tissue, fat, and iron (b) bone mineral density in a trabecular bone composed of calcium hydroxyapatite, yellow, and red marrow . The three‐material decomposition method in DECT was extended to a framework that also includes the two‐material decomposition and tissue segmentation to quantify soft tissues in terms of their mass fractions of water, protein, and lipid . Another approach using image data from DECT is to determine electron densities and effective atomic numbers of the materials .…”

Parallelisation of the Model-Based Iterative Reconstruction Algorithm Dira

“…The soft tissue is then decomposed using three-material decomposition (MD3) and the bone is decomposed using two-material plus density decomposition (MD2) (4) , resulting in the decomposed volume . The material classification is done as follows.…”