Microbeam
A microbeam is a narrow beam of radiation, of micrometer or sub-micrometer dimensions. Together with integrated imaging techniques, microbeams allow precisely defined quantities of damage to be introduced at precisely defined locations. Thus, the microbeam is a tool for investigators to study intra- and inter-cellular mechanisms of damage signal transduction.
Essentially, an automated imaging system locates user-specified targets, and these targets are sequentially irradiated, one by one, with a highly-focused radiation beam. Targets can be single cells, sub-cellular locations, or precise locations in 3D tissues. Key features of a microbeam are throughput, precision, and accuracy. While irradiating targeted regions, the system must guarantee that adjacent locations receive no energy deposition.
History
The first microbeam facilities were developed in the mid-90s. These facilities were a response to challenges in studying radiobiological processes using broadbeam exposures. Microbeams were originally designed to address two main issues:[1]
- The belief that the radiation-sensitivity of the nucleus was not uniform, and
- The need to be able to hit an individual cell with an exact number (particularly one) of particles for low dose risk assessment.
Additionally, microbeams were seen as ideal vehicles to investigate the mechanisms of radiation response.
Radiation-sensitivity of the cell
At the time it was believed that radiation damage to cells was entirely the result of damage to DNA. Charged particle microbeams could probe the radiation sensitivity of the nucleus, which at the time appeared not to be uniformly sensitive. Experiments performed at microbeam facilities have since shown the existence of a bystander effect. A bystander effect is any biological response to radiation in cells or tissues that did not experience a radiation traversal. These "bystander" cells are neighbors of cells that have experienced a traversal. The mechanism for the bystander effect is believed to be due to cell-to-cell communication. The exact nature of this communication is an area of active research for many groups.
Irradiation with an exact number of particles
At the low doses of relevance to environmental radiation exposure, individual cells only rarely experience traversals by an ionizing particle and almost never experience more than one traversal. For example, in the case of domestic
Due to the
Charged particle microbeam
The first microbeam facilities delivered charged particles. A charged particle microbeam facility must meet the following basic requirements:[2]
- The beam spot size should be on the order of a few micrometres or smaller, corresponding to cellular or sub-cellular dimensions.
- Irradiations of living cells should take place at atmospheric pressure.
- Beam current must be reduced to levels such that targets may be irradiated with an exact number of particles with high reproducibility.
- An imaging system is required to visualize and register cellular targets.
- Cell positioning must have high spatial resolution and accuracy and precision.
- A particle detector with high efficiency must count the number of particles per target and switch off the beam after the desired number of particles have been delivered.
- Environmental conditions (humidity, for example) for cells must be maintained such that cells are under little or no stress.
Beam spot size
Beam spots with diameter down to about two micrometres can be obtained by collimating the beam with pinhole apertures or with a drawn capillary. Sub-micrometre beam spot sizes have been achieved by focusing the beam using various combinations of electrostatic or magnetic lenses. Both methods are used at present.
Vacuum window
A vacuum window is necessary in order to perform microbeam experiments on living cells. Generally, this is accomplished with the use of a vacuum-tight window of a polymer a few micrometres thick or 100-500 nm thick Silicon nitride.
Cell registration and positioning
Cells must be identified and targeted with a high degree of accuracy. This can be accomplished using cell staining and
Particle counters
Particles must be counted with a high degree of detection efficiency in order to guarantee that a specific number of
Other considerations
Living cells must be maintained under conditions that do not
X-ray microbeam
Some facilities have developed or are developing soft x-ray microbeams. In these systems,
Biological endpoint
Many biological endpoints have been studied including
Microbeam systems worldwide
Microbeam Facilities Worldwide[2] | Radiation Type/LET | Beam Spot Size on Cell | Running Biology? | |
---|---|---|---|---|
Radiological Research Accelerator Facility (RARAF),[3][4][5] Columbia University | any cation, x rays low to very high |
0.6 μm | yes | |
JAERI,[6][7][8] Takasaki, Japan | high |
yes | ||
Special Microbeam Utilization Research Facility (SMURF), Texas A&M | low |
no | ||
Superconducting Nanoscope for Applied nuclear (Kern-)physics Experiments (SNAKE),[9] University of Munich | From p to HI 2-10000 keV/μm |
0.5 μm | yes | |
INFN-LABEC,[10] Sesto Fiorentino, Florence, Italy | p, He, C other ions | 10 μm for 3 MeV p | no | |
INFN-LNL[11] Legnaro, Italy | p, 3He+,++,4He+,++ 7-150 keV/μm |
10 μm | yes | |
CENBG, Bordeaux, France | p, α Up to 3.5 MeV |
10 μm | ||
GSI,[12] Darmstadt, Germany | From α to U-ions Up to 11.4 MeV/n |
0.5 μm | yes | |
IFJ,[13] Cracow, Poland | p - Up to 2.5 MeV x ray - 4.5 keV |
12 μm 5 μm |
yes | |
LIPSION,[14] Leipzig, Germany | p, 4He+,++ Up to 3 MeV |
0.5 μm | yes | |
Lund NMP,[15] Lund, Sweden | p Up to 3 MeV |
5 μm | ||
CEA-LPS,[16] Saclay, France | p 4He+,++ Up to 3.75 MeV |
10 μm | yes | |
Queen's University, Belfast, Northern Ireland UK | x ray 0.3-4.5 keV |
< 1 μm | yes | |
University of Surrey, Guilford, UK | p, α, HI | 0.01 μm (in vacuum) | yes | |
PTB,[17] Braunschweig, Germany | p, α 3-200 keV/μm |
< 1 μm | yes | |
Single Particle Irradiation System to Cell (SPICE),[18][19][20][21] National Institute of Radiological Sciences(NIRS), QST, Japan | p 3.4 MeV |
2 μm | yes[22][23][24] | |
W-MAST, Tsuruga, Japan | p, He | 10 μm | no | |
McMaster University, Ontario, Canada | no | |||
Nagasaki University, Nagasaki, Japan | x-rays 0.3-4.5 keV |
< 1 μm | yes | |
Photon Factory,[25][26] KEK, Japan | x-rays 4-20 keV |
5 μm | yes | |
CAS-LIBB, Institute of Plasma Physics,[27][28] CAS, Hefei, China | p 2-3 MeV |
5 μm | yes | |
Centro Atómico Constituyentes, CNEA, Buenos Aires, Argentina | to H from U 15 MeV |
5 μm | yes | |
FUDAN University,[29] Shanghai, China | p,He 3 MeV |
2 μm | yes | |
Institute of Modern Physics[30] CAS, Lanzhou, China | ||||
Gray Laboratory, London | low, high | Yes | ||
Gray Laboratory, London | soft X | Yes | ||
PNL, Richland, Washington | low | Yes | ||
Padua, Italy | soft X | Yes | ||
MIT Boston | low, high | Yes | ||
L'Aquila, Italy | high | No | ||
LBL, Berkley | very high | No | ||
University of Maryland | low | Yes | ||
Tsukuba, Japan | soft X | Yes | ||
Nagatani, Japan | low, high | Yes | ||
Seoul, South Korea | low | Yes | ||
Helsinki, Finland | high | No | ||
Chapel Hill, North Carolina | low | No | ||
Gradignan, France | high | Yes |
Microbeam Workshops
There have been nine international workshops, held approximately once every two years, on Microbeam Probes of Cellular Radiation Response. These workshops serve as an opportunity for microbeam personnel to come together and share ideas. The proceedings of the workshops serve as an excellent reference on the state of microbeam-related science.
International Workshops on Microbeam Probes of Cellular Radiation Response | Year | Number of Microbeams |
---|---|---|
Gray Laboratory, London[1] | 1993 | 3 |
Pacific Northwest Labs, Washington | 1995 | 3 |
Columbia University, New York | 1997 | 4 |
Dublin, Ireland[31] | 1999 | 7 |
Stresa, Italy[32][33] | 2001 | 12 |
Oxford, England[34] | 2003 | 17 |
Columbia University, New York[35] | 2006 | 28 |
NIRS, Chiba, Japan[36] | 2008 | 31 |
GSI, Darmstadt, Germany | 2010 | |
Columbia University, New York | 2012 | |
Bordeaux, France [1] | 2013 | |
Tsuruga, Fukui, Japan [2] | 2015 | |
Manchester, UK [3] | 2017 |
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