Abstract ID: 94 Development of a methodology for formulating radiologically equivalent materials to human tissues

Abstract

The study and development of phantom materials is central to the calculation of patient doses in medical imaging applications. To ensure tissue-equivalence, these materials should have radiation attenuation and scattering properties similar to water or human tissues [ 1 Hermanm K.P. et al. Phys Med Biol. 1985; 30: 1195-1200 Crossref PubMed Scopus (43) Google Scholar , 2 Homolka et al. Phys Med Biol. 2002; 47: 2907-2916 Crossref PubMed Scopus (15) Google Scholar , 3 White D. R Phys Med Biol. 1977; 22: 219-228 Crossref PubMed Scopus (81) Google Scholar ]. Additionally, Monte Carlo techniques are useful to evaluate the radiation transmission and scattering properties of different formulations in order to assure their tissue equivalence when compared with real tissues. In this work the authors evaluate the use of the least squares method as a tool to optimize the formulation of phantom materials. There were developed water-equivalent materials for diagnostic imaging energy range (10–150 keV) as well as mammography phantom formulations for different glandular/adipose breast tissue compositions [ [4] Hammerstein et al. Radiol V. 1979; 130: 485-491 Crossref PubMed Scopus (489) Google Scholar ] for the energy range 8–28 keV. The developed materials are constituted by a thermoplastic base and some additives. The methodology consisted in fitting by the Least Square Method the volume fractions of the components of the phantom material in order to make their linear attenuation coefficient [ [5] Hubbel J.H. Seltzer S.M. 2004, Available:http://physics.nist.gov/xaamdi. Google Scholar ] as close as possible to the linear attenuation coefficient of the reference material such as breast tissue or water. A weight function which reflects the contribution of the X-ray spectra in the suitable energy range was also introduced. The weight function used represents the standard radiation spectra qualities RQR10 and RQR-M2 according to TRS 457 (IAEA) [ [6] IAEA TRS 457 Vienna. 2011. Google Scholar ]. The transmitted and scattered X-ray spectra of the developed compositions were simulated as well as their dose profiles using the PENELOPE Monte Carlo code. The linear attenuation coefficient obtained using the least squares method is in good agreement with the reference material for both water and breast tissue with relative differences lower than 2%. The Monte Carlo method is very useful in determining the X-ray transmission and scattering properties of the materials, before the manufacture of the physical phantom. The study and development of phantom materials is central to the calculation of patient doses in medical imaging applications. To ensure tissue-equivalence, these materials should have radiation attenuation and scattering properties similar to water or human tissues [ 1 Hermanm K.P. et al. Phys Med Biol. 1985; 30: 1195-1200 Crossref PubMed Scopus (43) Google Scholar , 2 Homolka et al. Phys Med Biol. 2002; 47: 2907-2916 Crossref PubMed Scopus (15) Google Scholar , 3 White D. R Phys Med Biol. 1977; 22: 219-228 Crossref PubMed Scopus (81) Google Scholar ]. Additionally, Monte Carlo techniques are useful to evaluate the radiation transmission and scattering properties of different formulations in order to assure their tissue equivalence when compared with real tissues. In this work the authors evaluate the use of the least squares method as a tool to optimize the formulation of phantom materials. There were developed water-equivalent materials for diagnostic imaging energy range (10–150 keV) as well as mammography phantom formulations for different glandular/adipose breast tissue compositions [ [4] Hammerstein et al. Radiol V. 1979; 130: 485-491 Crossref PubMed Scopus (489) Google Scholar ] for the energy range 8–28 keV. The developed materials are constituted by a thermoplastic base and some additives. The methodology consisted in fitting by the Least Square Method the volume fractions of the components of the phantom material in order to make their linear attenuation coefficient [ [5] Hubbel J.H. Seltzer S.M. 2004, Available:http://physics.nist.gov/xaamdi. Google Scholar ] as close as possible to the linear attenuation coefficient of the reference material such as breast tissue or water. A weight function which reflects the contribution of the X-ray spectra in the suitable energy range was also introduced. The weight function used represents the standard radiation spectra qualities RQR10 and RQR-M2 according to TRS 457 (IAEA) [ [6] IAEA TRS 457 Vienna. 2011. Google Scholar ]. The transmitted and scattered X-ray spectra of the developed compositions were simulated as well as their dose profiles using the PENELOPE Monte Carlo code. The linear attenuation coefficient obtained using the least squares method is in good agreement with the reference material for both water and breast tissue with relative differences lower than 2%. The Monte Carlo method is very useful in determining the X-ray transmission and scattering properties of the materials, before the manufacture of the physical phantom.