Development of a line electron focusing lens for carbon nanotube field emission based microbeam radiation device

Abstract

Microbeam radiation therapy (MRT) is an experimental and preclinical technique with demonstrated capability of eradicating tumors while sparing normal tissues from radiation damage. We have proposed the design of a microbeam radiation device using a carbon nanotube (CNT) field emission x-ray source. The key enabling technology is the CNT based spatially distributed x-ray technology. The proposed MRT system has a unique square system geometry with the radiations shining on the targeting tumor positioned at the center of the square. A high microbeam dose rate is achieved by distributing the electron energy over multiple elongated focal tracks with a significantly larger area and therefore higher heat capacity compared to a conventional x-ray source with a point focal spot. Meanwhile the efficiency of the xray photons going through the narrow microbeam collimator, thus the dose rate, is greatly increased by making the effective width of the focal track comparable to that of the microbeam collimator opening. In order to achieve the desired focal track on the anode, a commercial software package (Opera 3D, Cobham plc) was used to simulate and design the optimal line focusing lens. The finalized design was based on a two-electrode Einzel focusing lens configuration. The simulation shows the two-stage electrostatic focusing lens is capable of providing the 100μm effective focal spot size required for the proposed microbeam x-ray with 100μm beam width. The recent focal spot size measurement performed using a testing x-ray chamber has also verified the simulation results.