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Development of An Einzel Electron Focusing Lens for Microbeam Radiation Therapy Device

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J Zhang

J Zhang1*, J Lu2, O Zhou2, S Chang3, (1) Shanghai Advanced Research Institute, Shanghai, Shanghai, (2) University of North Carolina at Chapel Hill, Chapel Hill, NC, (3) UNC School of Medicine, Chapel Hill, NC

TU-E-108-9 Tuesday 2:00PM - 3:50PM Room: 108

Purpose:
The purpose of this work is to develop a novel Einzel electron focusing lens for carbon nanotube (CNT) field emission based microbeam radiation therapy (MRT). The CNT cathode used for the proposed microbeam radiation source has a unique linear cathode profile so that the focusing structure needs to be optimized in order to achieve the desired focal spot size for efficient generation of microbeam radiation.

Methods:
The proposed design of the MRT device has a square system configuration with four independent linear x-ray tube modules. Each tube module includes a linear carbon nanotube field emission cathode array, which is the core component of the MRT device. The CNT cathode is comprised of 5 individually controlled CNT cathode segments, each of which has a dimension of 2.5mmx30mm. A commercial software package (Opera 3D, Cobham plc) was used to simulate and design the optimal focusing structure. A full scale computer model covering the entire electron beam path was constructed for the electron optical simulation.

Results:
Based on the simulation, the two-stage electrostatic focusing lens is capable of providing the 102um focal spot size required for the proposed microbeam radiation therapy treatment with 100um beam width. Based on our simulation results, we are able to achieve over 65% electron beam transmission rate. Both results were verified experimentally using a small scale testing x-ray chamber.

Conclusion:
We have designed a novel Einzel electron focusing lens to achieve the desired focal spot in order to improve the efficiency of microbeam generation, thus the dose rate. The simulation and experiment show the two-stage electrostatic focusing lens is capable of providing a 102um effective focal spot size. Meanwhile we have also demonstrated reasonable electron beam transmission rate (>65%), which is critical in terms of achieving high x-ray output.

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