Development of an Electron Development of an Electron Microbeam for Cell Culture StudiesMicrobeam for Cell Culture Studies

T. W. Botting, L. A. Braby, and J. R. Ford

Texas A&M University

OverviewOverview

BackgroundConstructionOperationCurrent ExperimentsFuture

ObjectiveObjective

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?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 dosebeam delivery of electron dose

Targeting• irradiation paths• discrete locations

Dose• duration• intensity

Energy

Electron Beam ProductionElectron 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 DeliveryBeam Delivery

Collimator Assembly• capillary tube• swivel mounts for alignment

Cell dish stage• x-y motion control

Microscope and camera• targeting

Electron Microbeam ApparatusElectron 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 AcceleratorSource and Accelerator

- Source- Source

- Accelerator tube- Accelerator tube

Voltage dividers -Voltage dividers -

\\Faraday Cup controlFaraday Cup control

Turbo pump -Turbo pump - Equipotential ringsEquipotential rings//

3D Schematic3D Schematic

Collimator Stand and MicroscopeCollimator Stand and Microscope

X-Y motion controlX-Y motion control||

CCD camera -CCD camera -

- Stage- Stage

\\ Capillary CollimatorCapillary Collimator

Light SourceLight Source//

Cell culture dishesCell culture dishes

Final Construction DetailsFinal Construction Details

Voltage dividers• 30 M per tube section for smooth gradient

Exit collimation• 5m and 300m exit aperatures

Exit window• 2m thick mylar (same as cell dishes)

OperationOperation

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 ImprovementsDesired Improvements

Beam stabilityBeam currentBeam transmission

Bystander Effect ExperimentsBystander Effect Experiments

Irradiate nearly confluent cellsCDKN1A 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…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