title: Monte Carlo based water/medium stopping-power ratios for various ICRP and ICRU tissues.
abstract: Water/medium stopping-power ratios, s(w,m), have been calculated for several ICRP and ICRU tissues, namely adipose tissue, brain, cortical bone, liver, lung (deflated and inflated) and spongiosa. The considered clinical beams were 6 and 18 MV x-rays and the field size was 10 x 10 cm(2). Fluence distributions were scored at a depth of 10 cm using the Monte Carlo code PENELOPE. The collision stopping powers for the studied tissues were evaluated employing the formalism of ICRU Report 37 (1984 Stopping Powers for Electrons and Positrons (Bethesda, MD: ICRU)). The Bragg-Gray values of s(w,m) calculated with these ingredients range from about 0.98 (adipose tissue) to nearly 1.14 (cortical bone), displaying a rather small variation with beam quality. Excellent agreement, to within 0.1%, is found with stopping-power ratios reported by Siebers et al (2000a Phys. Med. Biol. 45 983-95) for cortical bone, inflated lung and spongiosa. In the case of cortical bone, s(w,m) changes approximately 2% when either ICRP or ICRU compositions are adopted, whereas the stopping-power ratios of lung, brain and adipose tissue are less sensitive to the selected composition. The mass density of lung also influences the calculated values of s(w,m), reducing them by around 1% (6 MV) and 2% (18 MV) when going from deflated to inflated lung.
authors.affiliation: Facultat de Física (ECM), Universitat de Barcelona, Diagonal 647, Barcelona, Spain. jose@ecm.ub.es
authors.forename: José M
authors.initials: JM
authors.lastname: Fernández-Varea
authors.forename: Pablo
authors.initials: P
authors.lastname: Carrasco
authors.forename: Vanessa
authors.initials: V
authors.lastname: Panettieri
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Brualla
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism / Q000473:pathology*; D003198:Computer Simulation; D004583:Electrons; D008168:Lung / Q000473:pathology; D015233:Models, Statistical; D008962:Models, Theoretical; D009010:Monte Carlo Method; D010315:Particle Accelerators; D017785:Photons; D011878:Radiotherapy / Q000379:methods*; D011879:Radiotherapy Dosage; D012015:Reference Standards; D014018:Tissue Distribution; D014867:Water / Q000737:chemistry; D014965:X-Rays
chemical_list: D014867:Water