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DNA double-strand breaks in human cancer cells demonstrated by the irradiation of laser-accelerated protons
- toward the development of laser-driven cancer-therapy accelerator -

Apr. 23, 2009

The collaborative team of Japan Atomic Energy Agency, Osaka University, Hyogo Ion Beam Medical Center, Central Research Institute of Electric Power Industry, Nippon Advanced Technology, and Shin-Nippon Biomedical Laboratories has developed a laser-driven ion irradiation apparatus for radiobiological study and successfully demonstrated DNA double-strand breaks of in-vitro human lung cancer cells by laser-accelerated protons.

In these several decades, high-frequency ion accelerators have been used for ion-beam cancer therapy. Recently, high-intensity lasers have been suggested as a potential cost-saving alternative to conventional ion accelerators for the radiotherapy. A unique feature of laser acceleration is the extremely high peak current attributed mostly to the short duration of a single proton bunch. However, there has been no experimental work investigating biological effects of such high-current, short-bunch laser-driven ion beams.

We have developed a laser-driven ion irradiation apparatus for biological studies that experimentally reproduces the fundamental interactions between laser-accelerated protons and cancer cells in patientsEbody (Fig. 1). This apparatus delivers ~ 2.5×104 laser-driven protons onto a 1 mm2 cultured (in-vitro) cell layer within a time interval of only 15 ns. We then estimate the proton flux to be~103 mm-2 ns-1. Compared with the case of ion beam therapy by conventional accelerators, the dynamics differ by seven orders of magnitude for these cases. We show the result of DNA double-strand breaks of in-vitro human lung cancer cells (A549) in Fig. 2. This fact indicates that the laser-driven protons are applicable for the ion-beam cancer therapy. The laser-driven table-top ion-irradiation apparatus will open a new field of radiobiological science and applications.

This work is supported by Special Coordination Funds for Promoting Science (SCF) and “Mono-energetic quantum beam science with PW lasersEproject commissioned by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. This work has been published on the official journal of American Institute of Physics, Applied Physics Letters 94, 181502 (2009).

FIG.1: Newly-developed laser-driven proton irradiation system for radiobiological studies
High-intensity laser pulses are generated by J-KAREN laser system and focused onto thin plastic foils supplied by a target-driver. The laser focal spot itself works as a “micron-sizedEproton accelerator. The proton beams are selected by the magnetic fields and irradiate cancer cells cultured in a capsule.

FIG.2: Result of laser-accelerated proton irradiation onto in-vitro human lung cancer cells.
Cancer cell nuclei irradiated with the protons are stained with green color indicating the generation of DNA double-strand breaks.

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