QST generates high-energy electron beam via laser irradiation: Expectations for shielding-free radiation therapy

A research group led by Senior Principal Researcher Michiaki Mori at the Kansai Institute for Photon Science, Quantum Science and Technology Department of the National Institutes for Quantum Science and Technology (QST), in collaboration with Professor Toshiki Tajima of the University of California, Irvine, and the University of Waterloo, Canada, announced that they have generated high-energy electron beams, a type of radiation, via laser irradiation from a microcapillary hole. This is expected to be applied to endoscopic radiation (electron beam) generators to reduce radiation dose and enable radiation cancer treatment that does not require shielding. Results were published in the international academic journal AIP Advances on March 28.

Radiation therapy for cancer is attracting attention as a treatment that allows a high quality of life because it does not involve surgery, which is hard on the patient's body. However, the conventional irradiation method cannot avoid exposing the patient to radiation until it reaches the affected area. The operator needs to pay attention to the radiation emissions associated with accelerator operation, and the problem is high operation costs.

Pulsed lasers, which emit light instantaneously, can generate stronger intensity (peak output) the shorter the emission time. Based on the same principle, the research group has been studying "laser plasma acceleration," in which a small tabletop laser device is used to generate laser pulses with high peak power, which are then focused down to the size of a micron to generate high-energy electrons and ions. This acceleration mechanism was proposed by Tajima (now a professor at the University of California, Irvine) in 1979.

This time, the research group aimed at highly efficient and practical acceleration of electrons using a very stable laser device without high peak power, based on the technology developed by QST. Previously, Tajima reported that plasma generated by a low peak power laser can be used to produce electron beams with sufficient energy for industrial, medical, and other applications. However, the aligned carbon nanotubes that were envisioned for irradiation for the aforementioned purpose presented many technical challenges for manufacturing. Therefore, they used a simpler commercially available microcapillary plate. These are made up of a a glass plate with numerous holes about one-tenth the size of a hair and were expected to be equally effective.

When the pulsed laser was irradiated to the microcapillary plate, it was confirmed that a high-energy electron beam at the level of several hundred kiloelectron volts was generated, which can be used to treat cancer. A microcapillary plate with approximately 6,000 10-µm holes in a 1-mm square was used. The group has demonstrated that even when the laser intensity is reduced 1/10th to 1/100th, which is approximately equal to the laser intensity used in femtosecond laser processing, electron beams with the energy necessary for medical applications, including cancer treatment, can be generated. If a device with a tiny microcapillary plate fixed to the tip of an optical fiber can be fabricated and used in combination with an endoscope, high-energy electron beams can be generated in close proximity to cancerous tissue in the body to provide radiation therapy. As radiation generation is limited to the tip of the optical fiber, it is expected to reduce the radiation dose, which has been a problem in existing radiation cancer treatment, and eliminate radiation shielding equipment, thereby making it possible to construct a low-cost cancer treatment device.

Mori said, "This research has the potential to substantially improve cancer treatment using conventional radiation sources. Although this is only the first step, we have obtained particularly good results. In the future, we intend to optimize the actual configuration of the necessary equipment and expand it, such as cell irradiation and animal experiments. The QST Kansai Institute for Photon Science is also developing the use of laser technology to miniaturize heavy-ion cancer therapy equipment."

Journal Information
Publication: AIP Advances
Title: Experimental realization of near-critical-density laser wakefield acceleration: Efficient pointing 100-keV-class electron beam generation by microcapillary targets
DOI: 10.1063/5.0180773