Premium
TU‐E‐BRB‐10: Investigation of the Water‐to‐Air Stopping Power Ratio for Carbon Ion Beam Dosimetry Based on Experimental Data and FLUKA Simulation
Author(s) -
SanchezParcerisa D,
Gemmel A,
Parodi K,
Jäkel O,
Rietzel E
Publication year - 2011
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 - 10.1118/1.3613186
Subject(s) - stopping power , dosimetry , monte carlo method , fluence , ionization , range (aeronautics) , bragg peak , ionization chamber , ion , beam (structure) , computational physics , particle therapy , physics , nuclear physics , atomic physics , materials science , irradiation , optics , nuclear medicine , statistics , mathematics , medicine , quantum mechanics , composite material
Purpose: Water‐to‐air stopping power ratio (Sw,air) is currently known with an uncertainty of 2% for carbon ion beams (IAEAˈs TRS‐398), and it is the main source of uncertainty in absolute dosimetry with air‐filled ionization chambers. We present here a more precise calculation of its value from measurements performed under controlled experimental conditions Methods: Sw,air is given in TRS‐398 as a particle fluence weighted average over all particles and energies, and it is derived from track‐lenght fluence of each particle in water and its mass stopping powers in water and air. All these quantities were calculated with the general‐purpose Monte Carlo code FLUKA. The input values to the code, including water and air mean ionization potentials of Iw = 75.9 ± 0.2 eV and Iair = 87 ± 3 eV, were chosen in accordance to experimental measurements of mono‐energetic carbon ion beams carried out at the Heidelberg Ion Therapy Center (HIT). The Sw,air was calculated for spread‐out Bragg Peaks (SOBPs) at different depths, and a possible dependence on the residual range was investigated. Results: For all the studied SOBPs, the uncertainty in the stopping power ratio could be reduced significantly by introducing a logarithmic dependence on the residual range. Moreover, using the fixed value of Sw,air =1.13 causes, on average, a dose underestimation of 0.1 % if used in the plateau area and of 0.4% if used n the peak (compared to Monte Carlo data), whereas using our Sw,air(z) model reduces this dose underestimation below 0.05% in all cases. Conclusions: The contribution presents a revised calculation of the water‐to‐air stopping power ratio using own experimental data that reduces significantly the uncertainty of the current reference value. The research leading to these results has received funding from the European Communityˈs Seventh Framework Programme 2007–2013 under grant agreement n° 215840‐2 (PARTNER).