Provider: National Science Library - National Research Council Canada / Bibliothèque scientifique nationale - Conseil national de recherches Canada
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TY - JOUR
TI - Towards a quantitative, measurement-based estimate of the uncertainty in photon mass attenuation coefficients at radiation therapy energies
DO - 10.1088/0031-9155/60/4/1641
AU - Ali, E. S. M.
AU - Spencer, B.
AU - McEwen, M. R.
AU - Rogers, D. W. O.
T2 - Physics in Medicine and Biology
SN - 0031-9155
SN - 1361-6560
VL - 60
IS - 4
SP - 1641
EP - 1654
AB - In this study, a quantitative estimate is derived for the uncertainty in the XCOM photon mass attenuation coefficients in the energy range of interest to external beam radiation therapy—i.e. 100 keV (orthovoltage) to 25 MeV—using direct comparisons of experimental data against Monte Carlo models and theoretical XCOM data. Two independent datasets are used. The first dataset is from our recent transmission measurements and the corresponding EGSnrc calculations (Ali et al 2012 Med. Phys. 39 5990–6003) for 10–30 MV photon beams from the research linac at the National Research Council Canada. The attenuators are graphite and lead, with a total of 140 data points and an experimental uncertainty of ~0.5% (k = 1). An optimum energy-independent cross section scaling factor that minimizes the discrepancies between measurements and calculations is used to deduce cross section uncertainty. The second dataset is from the aggregate of cross section measurements in the literature for graphite and lead (49 experiments, 288 data points). The dataset is compared to the sum of the XCOM data plus the IAEA photonuclear data. Again, an optimum energy-independent cross section scaling factor is used to deduce the cross section uncertainty. Using the average result from the two datasets, the energy-independent cross section uncertainty estimate is 0.5% (68% confidence) and 0.7% (95% confidence). The potential for energy-dependent errors is discussed. Photon cross section uncertainty is shown to be smaller than the current qualitative 'envelope of uncertainty' of the order of 1–2%, as given by Hubbell (1999 Phys. Med. Biol 44 R1–22).
PY - 2015
DA - 2015/01/26
PB - IOP Publishing
LA - eng
C1 - Collection / Collection : NRC Publications Archive / Archives des publications du CNRC
C2 - Record identifier / Identificateur de l’enregistrement : cd6bb15b-f4aa-4d1e-95bd-bbb3c49e1cb9
ER -