11-1 DNA Double-Strand Breaks of Human Cancer Cells by Irradiation with Laser-Accelerated Protons

-Toward Cancer Therapy by Laser-Driven Accelerators-

Fig.11-3 Newly-developed laser-driven proton irradiation system for radiobiological studies
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Fig.11-3 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 foil successively shifted by a target-driver. The laser focal spot is a "micron-sized" proton accelerator. The proton beams are separated by magnetic fields and irradiate cancer cells cultured in a capsule.

 

Fig.11-4 Result of laser-accelerated proton irradiation of in-vitro human lung cancer cells

Fig.11-4 Result of laser-accelerated proton irradiation of 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.

During these past 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 this radiotherapy. A unique feature of laser acceleration is the extremely high peak current given to a single proton bunch for a short duration. However, technical problems have prevented production of such high-current, short-duration laser-driven ion beams suited for investigating biological effects.

We have developed a laser-driven ion irradiation apparatus for biological studies that causes the desired fundamental interactions between laser-accelerated protons and human cancer cells in a vacuum (Fig.11-3). This apparatus delivers ~2.5×104 laser-driven protons onto a 1mm2 cultured (in-vitro) cell layer within a time interval of only 15ns. We estimated the proton flux to be ~103mm-2 ns-1. The peak current was seven times that in ion beam therapy by conventional accelerators. The DNA double-strand breaks of in-vitro human lung cancer cells (A549) are shown in Fig.11-4. These results indicate that laser-driven protons are applicable to ion-beam cancer therapy. This laser-driven table-top ion-irradiation apparatus will open a new field of radiobiological science, and many applications should be forthcoming.

This work was supported with Special Coordination Funds for Promoting Science (SCF) managed by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT).


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