Measurements of the targeting accuracy of the Gray Laboratory charged-particle microbeam

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Abstract

The charged-particle microbeam provides a unique opportunity to precisely control both the dose to individual cells and the localization of dose within the cell. In the Gray Laboratory, both the performance of the detection system and the targeting system has been assessed for 3.5 MeV 3He2+ ions. Using an 18 μm transmission scintillator and a photomultiplier tube as the particle detection system, detection efficiency is higher than 99%. When a 5 μm collimator is used, the overall targeting accuracy (which includes the error associated with target finding and alignment) is <2.8μm for 98.7% of hits.

Introduction

The charged-particle microbeam has been designed to enable cells in vitro to be irradiated individually with micron precision, and with a precise number of charged particles delivered to predetermined locations in each cell (such as the nucleus or cytoplasm).

One rationale for this approach is that it is possible to devise experiments that are a more realistic representation of the situation relevant to environmental and occupational exposures to charged-particles (e.g. from exposure to naturally occurring radon, and from neutrons within nuclear power stations) [1]. The situation within the body exposed to environmental condition is that virtually no cell receives more than one charged-particle [2]. Most recently, microbeams have been used to study the so-called `bystander effect' where un-irradiated cells are seen to respond to signals from nearby irradiated cells [3], [4], [5].

Recently several groups in Europe, USA, Japan and China are developing, or planning to develop an installation for the micro-irradiation of cells in vitro using charged particles [2], [6], [7], [8], [9], [10]. The biological interest in the use of microbeam stems from the potential to define the ionizing energy absorbed by a cell, in terms of particle position and number. Therefore, the spatial resolution of the beam and efficiency of the particle detector are central to the performance of a microbeam. This paper reports measurements made using CR39 track-etch plastic to assess the detection efficiency and targeting accuracy of the Gray Laboratory charged-particle microbeam. The overall accuracy will depend on the properties of the collimator assembly, the accuracy to which targets are identified and the stage positioning accuracy.

Section snippets

Methods and materials

Experiments have been performed using 3He2+ ions, accelerated by a 4 MV Van de Graaff accelerator to 3.5 MeV, and collimated by a borosilicate glass capillary to a micron size beam. The layout of the microbeam system is shown in Fig. 1. Prior to the point at which particles exit the vacuum, a 1 mm long borosilicate glass capillary with a 1, 1.5 or 5 μm bore collimator is installed vertically at the end of the beamline, and is motorised to move precisely in the vertical direction. The collimator

The detection efficiency of the microbeam

The ideal particle counting system should respond to every particle that traverses a cell, and ignore all signals not initiated by a traversing particle. Track-etch plastic has again been used to evaluate the detection efficiency of 3He2+ particles. Fig. 2 is an example of the image obtained by irradiating one particle per location on a 20 μm spaced grid pattern. For this experiment, a gap between the CR39 and the collimator enhances the influence of scattering, such that two particles

The targeting accuracy

The targeting accuracy depends on three independent factors: the properties of the collimator, the accuracy to which targets are identified (and their co-ordinates assigned), and the stage positioning accuracy.

Results and discussion

The aiming resolution is decided by three factors: the precision of sample stage movement, the resolution of the target location finding image system and the collimator performance. With regard to target location and stage positioning accuracy, the results show that 98.4% of targeted positions are within 1.5μm of the desired position and 96.4% within 1.25μm. As for the collimator performance, 99.1% of the irradiated particles are located within the radius of 2.5μm of the collimator centre.

Acknowledgements

The financial assistance of the Chinese Academy of Sciences is gratefully acknowledged. The authors would like to thank the Gray laboratory Cancer Research Trust for the opportunity to undertake this work.

References (12)

  • C.R. Geard et al.

    Nucl. Instr. and Meth. B

    (1991)
  • A.P. Fews et al.

    Nucl. Instr. and Meth.

    (1982)
  • D.J. Brenner et al.

    Radiat. Res.

    (1995)
  • M. Folkard et al.

    Int. J. Radiat. Biol.

    (1997)
  • H. Nagasawa et al.

    Cancer Res.

    (1992)
  • A. Deshpande et al.

    Radiat. Res.

    (1996)
There are more references available in the full text version of this article.

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