Development of an Electron Microbeam for Cell Culture Studies T. W. Botting, L. A. Braby, and J. R. Ford Texas A&M University

Overview Background Construction Operation Current Experiments Future

Objective Our main objective is to achieve a better understanding of the risk to human health due to everyday exposure to low doses of ionizing radiation.

Most occupational and public radiation exposures are due to x and  rays so concern is about the effects of small numbers of moderate energy electrons (10 to 1000 keV)

How do we study this directly? –Need source for low-to-moderate energy electrons –Need method to deliver them exactly where desired We have used an electron microbeam to try to quantify bystander effects produced by moderate energy electrons

 beam delivery of electron dose Targeting irradiation paths discrete locations Dose duration intensity Energy

Electron Beam Production Electron source low-power tungsten filament low voltage power supply isolation transformer Accelerator Tube custom-made 3-section ceramic equipotential rings high voltage power supply

Beam Delivery Collimator Assembly capillary tube swivel mounts for alignment Cell dish stage x-y motion control Microscope and camera targeting

Electron Microbeam Apparatus Less than 4 feet high Capillary-style collimator Accelerator tube up to 100,000 Volts to produce up to 100keV electrons

Source and Accelerator - Source - Accelerator tube Voltage dividers - \ Faraday Cup control Turbo pump - Equipotential rings Equipotential rings/

3D Schematic

Collimator Stand and Microscope X-Y motion control | CCD camera - - Stage \ Capillary Collimator Capillary Collimator Light Source /

Cell culture dishes

Final Construction Details Voltage dividers 30 M  per tube section for smooth gradient Exit collimation 5  m and 300  m exit aperatures Exit window 2  m thick mylar (same as cell dishes)

Operation Electron source provides electron beam up to 1 nanoamp on the Faraday cup Stable at up to 85 kV so far beams at up to 90kV Software control of targeting line traces discrete spots

Desired Improvements Beam stability Beam current Beam transmission

Bystander Effect Experiments Irradiate nearly confluent cells CDKN1A and PCNA versus distance AG 1522 human fibroblasts Clone 9 rat liver line RIE mouse intestine line HBEC human primary bronchial cells Micronuclei assay AG 1522 human fibroblasts

Some Future Directions… Further micronuclei assays Clone 9 rat liver line RIE mouse intestine line HBEC human primary bronchial cells NTEC Rat primary tracheal cells All three methods (CDKN1A, PCNA, micronuclei) Complete comparison matrix with our positive ion  beam results as a control