Development of an Electron Microbeam for Cell Culture Studies

1
Development of an Electron Microbeam for Cell
Culture Studies

• T. W. Botting, L. A. Braby, and J. R. Ford
• Texas AM University

2
Overview

• Background
• Construction
• Operation
• Current Experiments
• Future

3
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.
4
Most occupational and public radiation exposures
are due to x and g rays so concern is about the
effects of small numbers of moderate energy
electrons (10 to 1000 keV)
5
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

6
mbeam delivery of electron dose

• Targeting
• irradiation paths
• discrete locations
• Dose
• duration
• intensity
• Energy

7
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

8
Beam Delivery

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

9
Electron Microbeam Apparatus
Less than 4 feet high Capillary-style
collimator Accelerator tube up to 100,000 Volts
to produce up to 100keV electrons
10
Source and Accelerator
\ Faraday Cup control
Turbo pump -
Equipotential rings /
- Accelerator tube
Voltage dividers -
- Source
11
3D Schematic
12
Collimator Stand and Microscope
CCD camera -
Light Source /
- Stage
X-Y motion control
\ Capillary Collimator
13
Cell culture dishes
14
Final Construction Details

• Voltage dividers
• 30 MW per tube section for smooth gradient
• Exit collimation
• 5mm and 300mm exit aperatures
• Exit window
• 2mm thick mylar (same as cell dishes)

15
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

16
Desired Improvements

• Beam stability
• Beam current
• Beam transmission

17
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

18
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
  mbeam results as a control