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#HOW TO STOP UNNECESSARY TRIM IN TAJIMA PULSE FREE#
Having a high intensity at the focus, on the order of 10 18 W/cm 2, the leading edge of the pulse creates a plasma, a mixture of ions and free electrons, that the main part of the pulse interacts with. At the Lund High-Power Laser Facility, LWFA is used to accelerate electrons and is accomplished by focusing a high-power laser pulse onto a gas target. One of the laser-plasma based accelerator types is the laser wakefield accelerator 12, 16– 19 (LWFA). At the current stage, only electrons are relevant for radiotherapy, as the acceleration of other particle species are limited in beam quality, having too low energy to be clinically usable because of their limited tissue penetration. Laser-plasma based accelerators can, with some modifications, accelerate different particle species, such as electrons 12, positrons 13, protons 14 and ions 15. This has led to an interest in using laser-plasma based accelerators with stronger accelerating fields on the order of 100 GV/m, reducing the accelerating distance with several orders of magnitude for a given particle energy, which could result in a more compact and cost efficient solution. Furthermore, the low scattering may also allow for a higher dose conformality compared to photons 11.Īchieving a VHEE beam with a traditional radio frequency-based linear accelerator requires large and costly structures as the accelerating electric fields are limited due to electrical breakdown ( < 100 MV/m). The possibility for other irradiation schemes have recently been demonstrated, such as multi-field and intensity modulation 10.
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This does not require patient-specific apertures, saving time and reducing cost, and can have greater precision compared to multileaf collimators 9. Due to the relatively low scattering and high penetration this makes VHEE suitable for a pencil beam electromagnetic scanning technique to irradiate the tumor. Another more practical advantage is the possibility for beam steering that comes with VHEE. VHEE exhibits a more reliable dose deposition when there are inhomogeneities in the beam path and a sharper cut off in the dose depth profile, sparing healthy tissue more effectively 6.
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Compared to photons, VHEE have some advantages for more deeply seated tumors. However, studies have shown a potential for very high energy electrons (VHEE) 3, 4, ranging in energies from 50 to 250 MeV, in the treatment of lung cancers 5, 6, prostate cancers 6– 8, pediatric brain tumors and head and neck cancers 6. Over the past decades, electron beams have mainly been used for treatment of superficial lesions due to the limited range of available electron energies, approximately 4–25 MeV 1, 2. This was achieved with realistic constraints, including 23 cm of propagation through air before any dose deposition in the phantom. The phantom was irradiated from 36 different angles to obtain a dose distribution mimicking a stereotactic radiotherapy treatment, with a peak fractional dose of 2.72 Gy and a total maximum dose of 65 Gy. The electron beam was focused to control the depth dose distribution and to improve the dose conformality inside a phantom of cast acrylic slabs and radiochromic film. In this paper, we show transport and focusing of laser wakefield accelerated electron beams with a maximum energy of 160 MeV using electromagnetic quadrupole magnets in a point-to-point imaging configuration, yielding a spatial uncertainty of less than 0.1 mm, a total charge variation below 1 % and a focal spot of 2.3 × 2.6 mm 2.
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To produce an electron beam of sufficiently high energy to allow for a long penetration depth (several cm), very large accelerating structures are needed when using conventional radio-frequency technology, which may not be possible due to economical or spatial constraints. An electron beam of very high energy (50–250 MeV) can potentially produce a more favourable radiotherapy dose distribution compared to a state-of-the-art photon based radiotherapy technique.