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The development of medicine has been always been dependent on the evolution of our knowledge of physics. Imaging cells in our bodies using microscopy and broken bones using X-ray radiation are two well known examples but particle accelerators also have many important medical applications.
The History of the Particle Accelerator
The first working particle accelerator, built by Ernest O. Lawrence, came to existence in 1931 as part of the Manhattan Project. The two basic designs which were used to accelerate particles are still used today: the linac (linear accelerator) and the cyclotron. The Lawrence cyclotron was first used in clinical trials at the Lawrence Berkeley National Laboratory in 1954.
Currently there are around 30,000 particle accelerators dotted across the globe, with over 40 million medical patients having benefited, either by diagnosis or treatment, from almost 60 years of medical research using linear accelerators.
Using Radiation Therapy to Treat Cancer
Despite these impressive statistics, radiation therapy cannot deal with the complexity of tumors since it is ineffective against quiescent non dividing cells. A tumor is comprised of many clones of cancer cells which are different in their cycling time and in their genetic makeup, which makes them sensitive or resistant to drugs and radiation.
If a therapy, whether it be drug or radiation based, eliminates some of these cells, cancer stem cells will rise and reproduce the tumor. As a result, radiation therapy needs to adapt in order to increase its curative power.
How does Radiation Therapy Work?
The science which underpins how radiation therapy works is based on the interaction between the nature of the particle, such as X-rays, photons, electrons, protons or heavy ions such as carbon ions, and with tumors and normal cells.
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External beam radiations (X rays) are delivered by linacs in order to target a large area of the body, including the tumor and surrounding normal tissues. As a result they have a lot of side effects on rapidly growing tissues such as skin and bone morrow. Particle beams are also produced by linacs. Electron beams are useful for targeting shallow tumors in the eye and on skin.
Proton beams cause little damage to normal tissues and after deep penetration release of their energy, their use is still limited to certain types of cancer. Carbon ion radiation is active against the radio resistant tumors but their effect on normal tissues is a limiting factor and thus more research is necessary.
Laser Wakefield Plasma Acceleration (LWPA)
New ideas have been explored in order to improve the effectiveness of radiation therapy. In order to diminish the negative side effects which impact on normal tissues and also the frequency of secondary cancers, it is necessary to change the configuration of particle accelerators.
A new development in the design of particle accelerators is the plasma wakefield accelerator, using a beam or a laser. The laser wakefield plasma accelerator (LWPA), combined with electrons or protons, can increase the effectiveness of radiation on tumors and reduce side effects.
Plasma Therapy
Since the establishment of radiation therapy, the ultimate goal was and still is the generation of free radicals inside tumor cells in order to kill them. Another technology called plasma therapy was pioneered by Mounir Laroussi and works by sending electrons with very high velocities through gasses such as helium or air, generating free radicals of all kinds (oxygen and nitrogen derived) and producing ‘plasma bullets’.
This technique has already proven its effectiveness at killing in vitro cultured cancer cells. The key difference between this and other techniques is that free radicals are applied from the outside of cancer cells. Plasma therapy is also capable of breaking Alzheimer plaques.
Currently plasma therapy does not make use of particle accelerator technology. The combination of the two technologies could be interesting. The main problem is finding a solution of how to deliver plasma bullets to tumors deep in the body – a tubular probe capable of holding the plasma bullets like a waveguide may be the solution.
Using Wave-Particle Duality
Ever since de Broglie’s seminal work on wave-particle duality in the first half of the twentieth century, we have known that there is a wavelength associated with all particles.
The transmission electron microscope, which is based on the acceleration of electrons, makes use of de Broglie’s theory. Using the same concept in radiation cancer therapy may be in the future as all slow neutrons break the U235 nucleus.
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Recently the Casadevall team in New York found fungi surviving the Chernobyl incident. Melanized fungi can harness the energy of hard radiation which is lethal to humans. This observation has relevance to radiation resistant cancer cells.
Accelerator Mass Spectrometry and Proteomics
Particle accelerators have many other medical applications aside from in cancer therapy. Accelerator mass spectrometry (AMS) uses a large nuclear particle accelerator based on the Tandem Van De Graaff and is already replacing conventional Carbon-14 dating techniques.
The combination of the AMS with Carbon-14 labeled proteins in vitro and in vivo creates a technique for the identification of proteins which is 2,000 times more sensitive than the classical ELISA which has been used for decades. This speeds up the research in drug development and clinical trials.
The proteomics field grew up very quickly following the sequencing of the human genome and many other species (one Tera base sequences are expected in 2015), allowing many thousands of proteins to be analyzed and their synthesis to be monitored. AMS/Proteomics in its many versions (MALDI-TOF, SELDI-TOF, Tandem MS, TIMS and SSMS) are enriching and challenging our knowledge of the living world.
Particle accelerators are useful to treat plastics for cell culture in vitro, a technique widely used in medical research and drug development. Plasma accelerators are also used in dental care, the sterilization of instruments used in surgery and research, the 3D imaging of protons, in food packaging, the silver lining of heart valves, as well as disinfecting vegetables from E Coli and other bacteria.
Reading and Further Reading
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