Highlight in Physicsworld.com (2008 September, 19th)
Researchers from Italy, France and Germany have shown that a tabletop laser can be used to accelerate a beam of electrons suitable for use in radiotherapy. The group, led by Antonio Giulietti of the Institute for Physical Chemistry Processes in Pisa, believes that such laser-based particle acceleration could considerably reduce the size and simplify the operation of radiotherapy facilities.
In radiotherapy beams of photons, electrons, protons, neutrons or ions are used to destroy tumours by ionizing the atoms within the tumours’ DNA. Usually this involves irradiating the patient from a number of different directions in order to pinpoint the tumour, and in the case of deep tumours, using higher-energy particles. This inevitably leads to some damage of the healthy tissue surrounding the tumour.
Damage can be limited using a technique known as intraoperatory radiotherapy (IORT), which involves irradiating the patient just once with electrons. This occurs in the operating theatre right after the tumour has been surgically removed. The idea is to destroy tumour cells that the surgery has missed. Because they do not have to penetrate deeply, the electrons can be fewer in number and have a lower energy, which means that the accelerators employed can be smaller.
However, as Giulietti points out, IORT, like ordinary radiotherapy, still uses radiofrequency electric fields to accelerate the electrons, which requires a machine more than two metres high and over half a tonne in weight. The machine must be shielded from the operating theatre and any maintenance requires the shut down of the theatre. “This therefore limits the energy of the electrons that can be used in the technique,” he adds.
Giulietti and colleagues have shown that these problems can be overcome by using a laser rather than radiofrequency electric fields to accelerate the electrons.
At the SLIC laboratory in Saclay, France, the researchers fired ultra-short laser pulses onto a jet of gas, creating a plasma with a fluctuating electron density. The electric field generated by these fluctuations accelerated the free electrons within the plasma such that they had energies and spatial characteristics suitable for use in IORT. By then passing these electrons through a 2 mm–thick piece of tantalum (and therefore decelerating them rapidly) the researchers were able to create gamma–ray photons that could also be used in radiotherapy (Phys. Rev. Lett. 101 105002).
Because the laser beam can travel for several tens of metres without any appreciable loss, the laser itself can be located outside the operating theatre. According to Giulietti, the only thing that would need to be in the theatre is a metallic box perhaps 50 by 20 by 20 cm across that would convert the laser beam into the electron beam, and which would contain a roughly 10 cm–long device to generate the gas jet and focusing optics of a similar size.
Intense γ-Ray Source in the Giant-Dipole-Resonance Range Driven by 10-TW Laser Pulses
A. Giulietti,1,2 N. Bourgeois,3 T. Ceccotti,4 X. Davoine,5 S. Dobosz,4 P. D'Oliveira,4 M. Galimberti,1 J. Galy,6 A. Gamucci,1,2 D. Giulietti,1,2,7 L. A. Gizzi,1,2 D. J. Hamilton,6 E. Lefebvre,5 L. Labate,1,2 J. R. Marquès,3 P. Monot,4 H. Popescu,4 F. Réau,4 G. Sarri,1 P. Tomassini,1,8 and P. Martin4,
Phys. Rev. Lett. 101, 105002 (2008)
1Intense Laser Irradiation Laboratory, IPCF, Consiglio Nazionale delle Ricerche, CNR Campus, Pisa, Italy
2INFN, Sezione di Pisa, Italy
3Laboratoire pour l'Utilisation des Lasers Intenses, CNRS UMR 7605, Ecole Polytechnique, Palaiseau, France
4CEA-DSM/IRAMIS/SPAM, Gif sur Yvette Cedex, France
5Département de Physique Théorique et Appliquée, CEA/DIF, 91680 Bruyères-le-Châtel, France
6European Commission, JRC Institute for Transuranium Elements, Karlsruhe, Germany
7Dipartimento di Fisica, Università di Pisa, Pisa, Italy
8INFN, Sezione di Milano, Italy