Microscope image of a vertical slice through a skin-tissue model showing the range of penetration depths calculated for 25-, 50-, and 90-keV electron beams. The centers of the bars mark the depths at which half of the electrons are expected to stop. Approximate widths of the three layers in the epidermis are indicated. |
Research
involving selective irradiation of a human skin tissue model is
improving how scientists determine the overall effects of low doses of
ionizing radiation such as might be received during certain medical
procedures or occupational exposures.
Scientists
at Washington State University-Tri Cities and Pacific Northwest
National Laboratory are modeling electron energy deposition patterns as
produced by a electron microbeam developed at PNNL to determine how it
may be used in the study of more complex biological systems.
Cells growing as a monolayer in a Petri dish are frequently used for
determining responses to environmental insults such as radiation.
However, this model does not include cell-cell and cell-matrix
interactions critical to maintaining tissue homeostasis. Using a more
realistic and complete tissue model is critical to the development of a
mechanistic understanding of the cellular radiation responses that occur
in vivo.
In
this study, the WSU-TC and PNNL scientists used an artificial skin
model made of normal human epidermal skin cells and connective tissue
cells called fibroblasts. The advantage of the model is that it has a
well-defined cellular composition that scientists can modify to gain a
fundamental understanding of how different cell types interact following
irradiation. This understanding will help development of biologically
based risk models and help ensure that radiation protection standards
are adequate and appropriate.
In
a series of recent papers, fluorescent and confocal microscopy images
have been used to characterize the detailed cellular morphology of the
skin tissue model. Using these images as a guide, Monte Carlo
simulations have been performed to establish the energy deposition
patterns on the microscopic scale. The computer simulations determined
the feasibility of selectively irradiating only the epidermal layer
using the PNNL-developed electron microbeam. Microbeams provide a
convenient way to investigate radiation-induced bystander effects.
Bystander effects are responses in unirradiated cells that are triggered
by signals received from irradiated neighboring cells.
Results
of the computer simulation suggest that the skin-tissue model epidermis
can be irradiated without significant exposure to the dermal layer.
This is because of the energy dependence of the electron microbeam’s
penetration of the skin sample. The result is a more realistic radiation
energy deposition scenario.
Now
that the scientists are confident that selective irradiation of the
epidermis of skin tissue is feasible using the PNNL electron microbeam,
they will begin using this device to understand the role of particular
cell types in the radiation-induced response.
The work was supported by the Department of Energy’s Low Dose Radiation Research Program. The research team includes John Miller and Atef Suleiman, WSU-TC; and Marianne Sowa, Xihai Wang and Will Chrisler, PNNL.
References:
Miller
JH, A Suleiman, WB Chrisler, and MB Sowa. 2011. “Simulation of
Electron-Beam Irradiation of Skin Tissue Model.” Radiation Research
175(1):113-118. doi: 10.1667/RR2339.1
Miller
JH, WB Chrisler, X Wang, and MB Sowa. 2011. “Confocal microscopy for
modeling electron microbeam irradiation of skin.” Radiation and
Environmental Biophysics (in press).
