201710090138長照2.0JAEA2010 光療Photo-Medical Research Cooperation 日本京都大學:::超迷你微創PDT''雷射內視鏡::LCT
Photo-Medical Research Cooperation
Toward Development of a Laser-Driven Ion Beam Apparatus
Fig.5-1 The current ion beam medical facility and outline of a laser-driven ion beam apparatus
Fig.5-2 Common research initiative for creation of a “Photo-Medical Valley”
The JAEA Photo-Medical Research Center (PMRC) is promoting innovative development of a laser-driven ion beam apparatus for medical applications. This device employs ion acceleration by a high power laser in order to significantly reduce overall size and cost, which can then facilitate wider access to ion beam cancer treatment (Fig.5-1).
The PMRC project has been pursued since 2007 in collaboration with ten partners (Fig.5-2), and is funded by the Special Coordination Fund for Promoting Science and Technology commissioned by the Ministry of Education, Culture, Sports, Science and Technology.
Development of a treatment and diagnostic device
To advance development of a laser-driven ion beam medical device, we conducted research and development to produce a proton beam suitable for cancer therapy. We verified the world’s first laser-driven ion acceleration method using a nanoparticle target. This research mainly targeted a key for the success of the PMRC project, namely a significant increase in the number of accelerated protons. Laser irradiation of nanoparticle targets has accelerated ions to maximum energies that exceed 20 MeV per nucleon (Topic 5-1). We also conducted studies of other target types and laser irradiation conditions. Thin film targets have yielded protons that were accelerated up to kinetic energies of 14 MeV.
Verification of the effects of treatment with a laser-driven proton beam
To verify that a laser-driven proton beam can be effective in cancer therapy, we completed experiments to determine the effect of proton irradiation of cancer cells. For the first time in the world, we successfully induced DNA double strand breaks in human-derived cancer cells by irradiating them with laser-driven proton beams. We also evaluated the biological effect of cell irradiation and measured self-activated gamma emission from phantom targets using a proton irradiation research chamber. This apparatus was built at the Hyogo Ion Beam Medical Center to determine if there is any difference in the irradiation effect between a laser-driven ion beam and an ion beam delivered by an existing accelerator.
Studies toward prototype development
As part of our efforts with industrial applications, we investigated the specifications of equipment and implementation of proton-induced radio-activation to study wear on metal surfaces. We also initiated clinical tests of a minimally invasive fiber-based medical device, together with development of integrated software to smoothly control it.
Based on these results, we will advance this project during this fiscal year and resubmit our proposal for program evaluation by the Special Coordination Fund for Promoting Science and Technology commissioned by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT).
5-2 Unlimited Particle Acceleration by Photon Pressure Was Proposed
－Synchronized Thin Foil Plasma Acceleration Due to Photon Pressure－
Fig.5-4 Laser piston acceleration of thin foil plasma
We have proposed a new theory, which points to the possibility of producing much higher energy particles using a modified laser piston method (Fig.5-4).
In the Photo-Medical Research Center (PMRC), laser driven particle acceleration is studied in order to make a compact particle cancer therapy machine, and it is necessary to realize theoretical calculations in the study. We must pay attention to laser piston acceleration, in which a thin foil is directly accelerated by the strong photon pressure generated by focusing a high peak power laser pulse on the foil. In conventional laser piston theory, the thin foil is accelerated while maintaining a constant areal density, as shown in the left figure in Fig.5-4. In this study, it was found that much higher energy can be obtained if we take into account a condition in which the areal density is decreased during the acceleration, even though the number of accelerated particles decreases. When the areal density of accelerated thin foil plasma is decreased, the velocity of the plasma is thought to become higher. This effect may cause the velocity of the thin plasma bulk to be almost the same as the velocity of laser propagation in the plasma. In such a case, the laser pulse cannot overtake the thin foil plasma, and continuously pushes the thin foil while locking this acceleration phase. Therefore, unlimited particle acceleration could be possible, imparting the momentum to the particles which constitute the thin foil plasma.
If we succeed in controlling areal density based on this theory, generation of the 200 MeV protons needed for cancer therapy is seen to be attainable by focusing a 200 TW laser pulse on a nanometer-size thin foil. The size of the laser driver could then be downscaled to be one fifth of the conventionally estimated scale.
This study is supported by the Special Coordination Fund (SCF) for Promoting Science and Technology commissioned by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT), and Grant-in-Aid for Scientific Research No. 20244065.
Bulanov, S.V. et al., Unlimited Ion Acceleration by Radiation Pressure, Physical Review Letters, vol.104, issue 13, 2010, p.135003-1－135003-4.