Physicists and physicians are both engaged in a seemingly relentless quest to build bigger machines to interact with ever-smaller targets with greater precision; the two fields are inextricably interwoven. Nobel Prize–winning physicist Marie Curie discovered radioactive elements and forms of radiation that are fundamental to the practice of medicine; this same radiation killed both Marie and her equally talented daughter. In 1959, Nobel Prize winner Richard Feynman described nanotechnology and nanoscale medical devices that are now in the process of revolutionizing medicine.
The Higgs boson is the elusive, highly sought after, as yet theoretical fundamental particle that physicists desperately need in order to tidy up one of their theories of how all things work. The boson is the last unobserved member of the particle family belonging to the standard model of physics. Physicists describe it as a rumor crossing a crowded room because it, too, causes transient clustering and massing in the wake of its passage. In essence, the boson is believed to be the fundamental particle that gives all other things—planets, people, and protons—mass.
If a large hadron collider, or LHC, sounds to you like something out of a science fiction movie, you’re not too far off. It is actually the gigantic nuclear particle accelerator and collider located outside of Geneva, Switzerland, at CERN, with which modern physicists plan to find the Higgs boson, using what amounts to an enormous ray gun. The LHC was built with the collaboration of more than 2,000 scientists and hundreds of separate universities and took 10 years to construct. The collider and its associated particle detectors, electron magnets and laboratories are housed in a 26.5-kilometer-long tunnel that is a little less than four meters in diameter and crosses the serpentine border between France and Switzerland several times. It lies at average depths of between 50 and 175 meters underground to minimize its impact on the environment and to prevent harmful radiation exposure to people walking on the land above. The discoveries made within that hidden tunnel will likely change our world above it irreversibly.
This giant machine is designed to fire one beam of protons traveling clockwise at another traveling counterclockwise—both beams at almost the speed of light—in hopes that information about debris from the resulting collision will explain some of the still-unanswered fundamental questions in physics. This a time honored way of finding things out that was invented by and has been practiced for centuries by boys. Fortunately, the proton is a generally well-behaved member of the hadron family (a class of particles composed of quarks), which also includes neutrons and mesons, and the large hadron collider is based on the design of older linear particle accelerators, or atom smashers, upon which, in turn, some of today’s medical radiation devices are modeled.
Over 1,600 superconducting magnets cooled with liquid helium are used to accelerate and steer the proton beams in the LHC. The energy developed in each of the circling proton beams is equivalent to that of a high-speed train traveling at 150 kilometers an hour. When the two beams of protons collide, an unimaginable amount of energy is released—in fact, the temperature at the contact point is a hundred thousand times hotter than the center of the sun. On the other hand, the cooling system for the magnets in the tunnel—the cryogenic distribution system—keeps parts of the collider at temperatures lower than that of outer space.
The protons in the beams make over 11,000 circuits of the tunnel every second, and the attendant forces are so powerful that there is at least a theoretical possibility that the proton collisions will produce microscopic black holes. This sounds really ominous but physicists reassure us that, if formed, these small black holes will deflate, like balloons, by blowing off energy through a process called Hawking radiation, named after the physicist Stephen Hawking.
Proton beam therapy describes the use of a beam of particles, exactly like the ones flying around the 26.5-kilometer hadron racecourse in Switzerland, to treat cancer in humans. Proton beam therapy is only available in a few places in the world. It differs from traditional radiation therapy in its use of beams of particles rather than x-ray waves for treatment. Unlike x-rays that deliver radiation to all the tissues along the path of the beam, causing a little bit of damage all along the way, proton beams pass harmlessly through the skin and overlying tissues to deliver their radiation into the target without injuring the surrounding tissues.
The first suggestion that protons might be used medically to treat tumors came from Robert R. Wilson, one of the physicists who worked on the Manhattan project with Albert Einstein, Richard Feynman and Robert Oppenheimer. A multidimensional scientist like Feynman (who sketched, painted, kept an office in a topless bar and played practical jokes), Wilson was also a sculptor, human rights advocate and a little bit of a rebel. Wilson described the potential for proton therapy in 1946. Having observed that proton beams fired from an accelerator give off a burst of radiation just before they come to a stop, he realized that a beam could be tuned to deliver energy to a very precise area, even one deep within the body.
Wilson proposed that bursts of protons could be trained, like horses, to gallop up to a tumor in formation and then stop on a dime (or on a pinpoint in the case of protons) to deliver their payload of radiation. It is instructive to contrast this elegant medical treatment with what happens in the hadron collider in Switzerland, where two columns of protons are smashed violently into one another at nearly the speed of light, shattering what we once thought were the fundamental particles—neutrons, protons and electrons—into still-smaller particles with names such as charm quark, strange quark, muon, gluon and baryon. In fact, all of the early proton treatments for medical disease were performed in particle accelerators originally built for physics research, such as the one at the Harvard Cyclotron Laboratory, which Wilson helped design, as well as devices in the Soviet Union, Switzerland, Japan and Sweden. The first accelerator built specifically for medical therapy wasn’t constructed until 1988.
FEATURE:
Inside the Cancer-Cell Smasher By William Hanson
Last modified 3/03/09