Highlights
- •Line-focus x-ray tubes are suitable for clinical microbeam radiation therapy (MRT) with very high dose rates.
- •With tracking simulations, a suitable setup for an electron source and beamline was found.
- •Additional electrostatic simulations ensure fields sufficiently low to avoid a field breakdown.
- •Thermal simulations identified mechanical displacements after heating up the cathode, which must be compensated.
Abstract
Microbeam radiotherapy (MRT) is a novel concept in radiation oncology with arrays
of alternating micrometer-wide high-dose peaks and low-dose valleys. Preclinical experiments
have shown a lower normal tissue toxicity for MRT with similar tumor control rates
compared to conventional radiotherapy. A promising candidate for the demanded compact
radiation source is the line-focus x-ray tube. Here, we present the setup of a prototype
for an electron accelerator being able to provide a suitable x-ray beam for the tube.
Several beam dynamic calculations and simulations were performed concerning particle
tracking, thermal and electrostatic properties of the electron source, resulting in
a proper beamline, including the cathode, the pierce electrode (PE) and the focusing
magnets. These parts are discussed separately.
The simulations showed that a rectangular cathode with a small width of 0.4mm is mandatory. To quickly shut down the electron beam, an additional voltage of
-600V must be applied to the PE. Moreover, the electric field inside the vacuum chamber
stays below 10MVm−1 to minimize the risk of field emission. The thermal simulation validates a small
displacement of 0.1mm of the heated cathode with respect to the PE, which must be considered during manufacturing
of the cathode-PE assembly.
The simulations lead to an adequate choice of cathode, electrodes and beamline to
achieve the required focal spot of with a beam current of 0.3A and an electron energy of 300keV. With this setup first MRT experiments with high dose rates up to 10Gys−1 can be executed.
Keywords
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Article info
Publication history
Published online: January 16, 2023
Accepted:
January 6,
2023
Received in revised form:
January 4,
2023
Received:
April 4,
2022
Identification
Copyright
© 2023 Associazione Italiana di Fisica Medica e Sanitaria. Published by Elsevier Ltd. All rights reserved.
