- Dielectric wall accelerator
The Dielectric Wall Accelerator (DWA) is a new compact particle accelerator designed at the Lawrence Livermore National Security, LLC (LLNS), managed Lawrence Livermore National Lab LLNL, a DOE National lab. It has been turned over to the UC Davis Cancer center supported by the UC Davis Crocker Nuclear Lab. It is designed to produce beams of bare atomic nuclei stripped of electrons--a hydrogen atom minus it's electron-- which is a proton, for use in External Beam Radiation Therapy EBRT. These charged particles are used to destroy cancer tumors inside the body.
Why a DWA is needed
The DWA addresses the main issues with the current proton therapy system—cost and size. Current proton cyclotrons (accelerators) cost $US180 million. These units are the size of a football field. The DWA is estimated to cost $20 million and will fit into a large room.
Types of External Beam Radiotherapy
The older type of radiotherapy is called x-ray, photon, electron, gamma-ray or cobalt-60. Charged particle therapy uses Linear Energy transfer LET to precisely place the energy on the target tumor. This energy damages both strands on the target cell's DNA which leads to cell apoptosis (death).
Charged Particles are superior to x-ray therapy
The current proton system is superior to the 100-year-old x-ray system known as IMRT. IMRT uses an indirect ionization of water in the cell to produce free radicals. These react chemically with the cell destroying single strands of the dual strand DNA.
Protons are many time heavier than electrons which makes them easier to control and allows them to more precisely target a tumor. Protons are charged particles and are accelerated to a predetermined (MeV) level which, using the bragg peak delivers the energy directly within 1–2 mm inside the tumor and stops. IMRT photons primarily indirectly ionizes the single strand DNA nuecleotide using the free radical method to disrupt cell life. Tumors are notorious for having a poor blood supply called cell (hypoxia). This requires the use of drugs to oxygenate the tumor. Since the tumor is fast growing it has a poor blood supply meaning any drugs directed at them will have difficulty getting to them.
The system is a spinoff of a DOE device to inspect nuclear weapons.
This system requires several new advances because of the high energies. A high gradient insulator  patent # 6,331,194. A wide band-gap photoconductive switch, about 4,000 are needed. A Symmetric Blumlein, typical width 1mm.
"A linac technology to accelerate protons to 100 MeV in 1 m is being developed at Lawrence Livermore National Laboratory. Originally developed for x-ray radiography to image explosives, the so-called dielectric wall accelerator generates a pulsed electric field that lasts a few nanoseconds. That proton-accelerating field propagates along an insulating wall at a controlled rate, says LLNL physicist George Caporaso. Compact Particle Acceleration Corp has licensed the technology and is now funding its development for proton therapy. Because the DWA is a pulsed linac, “it is easy to control not only the beam’s intensity but also its spot size and beam width,” says CPAC president Thomas Mackie. Commercial DWA systems are still in early development."
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