Page 299 - 2014 Printable Abstract Book
P. 299
material. The simulation consists of recording the energy and the path of the primary particle and all the
secondary particles generated during the process. This information can be used to assess the energy and
location of the energy deposited in the material which is further processed by radiation chemistry and
radiation biology to study the biological effectiveness of such radiation. Inelastic cross-sections for proton
and electron impacts on copper foils including both bulk and surface properties of the metallic copper
have been calculated and implemented into the Monte Carlo track structure code PARTRAC as a first step
towards simulations using more complex targets. Currently, simulations of the secondary electron
emission spectra from simple and combined copper-water targets including volume and surface areas are
performed and benchmarked against available experimental information to further improve the applied
transport models.
(PS5-22) Physical and Biological Characterization of a 137Cs Irradiator as the Reference for Studies of
Particle Relative Biological Effectiveness (RBE). Robert D. Stewart, PhD; Ning Cao, PhD; Geoffrey Linn, BS;
Jeff Schwartz, PhD; Juergen Meyer, PhD; George Sandison, PhD; and Eric Ford, PhD
University of Washington, Seattle, WA
Purpose: Test the hypothesis that the large variations in particle RBE reported in the literature
may be due to uncertainties associated with the physical and biological characterization of the reference
radiation. Methods: Uncertainties in dosimetry and the quantification of biological responses for the test
and reference radiation contribute to uncertainties in the inferred particle RBE. We measured cell survival
and number of chromosome breaks in monolayers of human foreskin fibroblast (HFF) cells and A549
137
human adenocarcinoma cells after a range of Cs doses. Ionization chamber measurements and Monte
Carlo (MCNP 6.1) simulations were used to quantify random and systematic errors in dose delivery. The
Monte Carlo Damage Simulation (MCDS) in combination with the Repair-Misrepair-Fixation (RMF) model
60
137
were used to estimate the RBE (relative to Co γ-rays) of several other radiations, including Cs, filtered
and unfiltered 20-300 kV x-rays (W, Mo and Rh anode). Results: Depth in culture medium (CM) has a
significant effect on the delivered dose to a cell monolayer. At least 1.8 mm of CM is required for full
60
137
buildup in a Cs beam, and 4.5 mm is needed for a Co beam. The absorbed dose at a depth of 1 mm is
3.4% less than that at a 1.8 mm depth. At depths shallower than 1 mm, the delivered dose to a cell layer
137
rapidly decreases (e.g., 30-40% lower dose at a depth of 0.7 mm). Dose corrections for Cs source transit
time into and out of position are significant below 0.5 Gy. The measured plating efficiencies (PE) of the
A549 and HFF cells in six replicate controls were 0.571 + 0.088 and 0.193 + 0.01, respectively. Simulations
60
predict an RBE (relative to Co) of 1.013 for 137 Cs, and an RBE of 1.17 (0.15 mm Cu filtration) to 1.3
(unfiltered) for 225 kVp x-rays. The type and amount of filtration, anode composition and x-ray tube
voltage also has a significant impact on x-ray RBE. Conclusion: The aggregate physical and biological
uncertainties in the quantification of biologically equivalent doses of a test and reference radiation may
easily approach 25-40% in monolayer cell culture experiments. Reports of particle RBE in the literature,
especially RBE values less than unity, need to be interpreted with caution, especially in inter-laboratory
60
137
comparisons in which x-rays are used as the reference radiation instead of Cs or Co γ-rays.
297 | P a g e
secondary particles generated during the process. This information can be used to assess the energy and
location of the energy deposited in the material which is further processed by radiation chemistry and
radiation biology to study the biological effectiveness of such radiation. Inelastic cross-sections for proton
and electron impacts on copper foils including both bulk and surface properties of the metallic copper
have been calculated and implemented into the Monte Carlo track structure code PARTRAC as a first step
towards simulations using more complex targets. Currently, simulations of the secondary electron
emission spectra from simple and combined copper-water targets including volume and surface areas are
performed and benchmarked against available experimental information to further improve the applied
transport models.
(PS5-22) Physical and Biological Characterization of a 137Cs Irradiator as the Reference for Studies of
Particle Relative Biological Effectiveness (RBE). Robert D. Stewart, PhD; Ning Cao, PhD; Geoffrey Linn, BS;
Jeff Schwartz, PhD; Juergen Meyer, PhD; George Sandison, PhD; and Eric Ford, PhD
University of Washington, Seattle, WA
Purpose: Test the hypothesis that the large variations in particle RBE reported in the literature
may be due to uncertainties associated with the physical and biological characterization of the reference
radiation. Methods: Uncertainties in dosimetry and the quantification of biological responses for the test
and reference radiation contribute to uncertainties in the inferred particle RBE. We measured cell survival
and number of chromosome breaks in monolayers of human foreskin fibroblast (HFF) cells and A549
137
human adenocarcinoma cells after a range of Cs doses. Ionization chamber measurements and Monte
Carlo (MCNP 6.1) simulations were used to quantify random and systematic errors in dose delivery. The
Monte Carlo Damage Simulation (MCDS) in combination with the Repair-Misrepair-Fixation (RMF) model
60
137
were used to estimate the RBE (relative to Co γ-rays) of several other radiations, including Cs, filtered
and unfiltered 20-300 kV x-rays (W, Mo and Rh anode). Results: Depth in culture medium (CM) has a
significant effect on the delivered dose to a cell monolayer. At least 1.8 mm of CM is required for full
60
137
buildup in a Cs beam, and 4.5 mm is needed for a Co beam. The absorbed dose at a depth of 1 mm is
3.4% less than that at a 1.8 mm depth. At depths shallower than 1 mm, the delivered dose to a cell layer
137
rapidly decreases (e.g., 30-40% lower dose at a depth of 0.7 mm). Dose corrections for Cs source transit
time into and out of position are significant below 0.5 Gy. The measured plating efficiencies (PE) of the
A549 and HFF cells in six replicate controls were 0.571 + 0.088 and 0.193 + 0.01, respectively. Simulations
60
predict an RBE (relative to Co) of 1.013 for 137 Cs, and an RBE of 1.17 (0.15 mm Cu filtration) to 1.3
(unfiltered) for 225 kVp x-rays. The type and amount of filtration, anode composition and x-ray tube
voltage also has a significant impact on x-ray RBE. Conclusion: The aggregate physical and biological
uncertainties in the quantification of biologically equivalent doses of a test and reference radiation may
easily approach 25-40% in monolayer cell culture experiments. Reports of particle RBE in the literature,
especially RBE values less than unity, need to be interpreted with caution, especially in inter-laboratory
60
137
comparisons in which x-rays are used as the reference radiation instead of Cs or Co γ-rays.
297 | P a g e
