Cancer remains one of the
leading causes of death around the world, with more than 10 million
cases diagnosed annually, including over 1.3 million new cases
diagnosed each year in the United States alone.
However, since the mid-twentieth century, when a diagnosis of cancer usually
amounted to a death sentence, many cancers have become much more controllable.
In the U.S., the National Cancer Institute’s goal of five-year survival
in more than 50 percent of cancer cases has been achieved. This is due in no
small measure to major advances in radiation oncology—now used either alone
or in combination with other therapies to treat up to 60 percent of all cancer
patients in the U.S.
At the center of many of these developments is Varian Medical Systems, formerly
known as Varian Associates and now the world’s leading supplier of technology
and systems for treating cancer with radiation therapy. Over a period of more
than 40 years, Varian has helped to establish and transform radiation oncology
through continuous evolution of its medical linear accelerator technology and
development of the world’s most comprehensive network of hardware, accessories,
and software for radiation therapy. Today, the company stands at the forefront
of a major revolution in cancer treatment.
The goal of radiation therapy is to destroy cancer cells by bombarding them with
X rays or electrons. The radiation damages the cancer cells, which later die
and are sloughed off by the body. Healthy cells that are exposed to moderate
amounts of radiation have the ability to repair themselves and survive. The challenge
that radiation oncologists face in every case is how to deliver enough X rays
to destroy the cancer without exceeding the level that the surrounding healthy
cells can tolerate. Solving this problem simply and effectively has been the
driving force behind most of the technological developments that have taken place
in radiation therapy over the last several decades.
The Early Years
Initially developed in the early 1900s, radiation therapy was used primarily
for relieving pain by shrinking tumors, but not often for cure. The earliest
radiotherapy devices used primitive X-ray tubes to generate very weak radiation—not
enough to effect cures or to penetrate the body very deeply. Next came cobalt
machines that offered higher energy but which delivered relatively slow treatments
that lengthened in time as the radioactive source within the machine weakened.
The weakened radioactive cobalt source also presented hospitals with a problem
of how to dispose of potentially dangerous radioactive waste.
A Technology Is Born
Modern radiation therapy traces its origins back to the invention of the “klystron” by
brothers Russell and Sigurd Varian in 1937. The Varian brothers first used
their invention in radar systems. However, after World War II, either the klystron
or the magnetron, another invention of the time, was used to propel charged
particles through a vacuum tunnel, resulting in a device called a linear accelerator
or linac. The linac was initially used for research in high energy physics.
In the early 1950s, Dr. Henry Kaplan, head of Stanford University’s Department
of Radiology, met with Edward Ginzton, a Stanford physicist and a Varian co-founder.
Kaplan proposed that a linac be specifically designed to generate high energy
X rays for the treatment of cancer. The idea was that klystrons would accelerate
electrons to near the speed of light. The electrons would then be made to strike
a tungsten target causing an emission of X rays of comparable energies. These
high-energy X-ray beams would then be used to bombard a cancerous tumor.
Even amongst the illustrious group of Stanford University researchers, Kaplan
and Ginzton were giants, according to Dr. Philip Rubin, Provost Emeritus for
Radiation Oncology at the University of Rochester Medical School and a pioneer
in the use of X rays against cancer.
“Henry Kaplan was a charismatic visionary who wanted to have an accelerator
in order to treat Hodgkin’s disease,” Dr. Rubin says. “Ginzton
was a man who transformed a complex research device into a practical clinical
tool. Together, they opened up a whole new universe for radiation therapy.”
The Kaplan-Ginzton meeting started a chain of research develop-ments that culminated
in 1960, when Varian introduced the “Clinac 6,” the first commercial
fully rotational radiotherapy linac. The Clinac 6 could generate sharply defined
beams of 6 MV X rays in a gantry that could be rotated 360 degrees around a
patient. Though limited in production, the Clinac 6 established that linacs
could be used to treat cancer, with intrinsic medical advantages over the cobalt
irradiators that had been used to treat cancer throughout the 1950s.
In 1968, Varian introduced the Clinac 4, a machine that deployed “standing
wave-guide” technology which, along with other advances, helped to reduce
the size, cost, and complexity of a medical linac. For the first time, the
linear accelerator technology became economically competitive with cobalt irradiators
and was ready to seize center stage. “The arrival of the Clinac 4 marked
the birth of modern radiation oncology,” says Dr. Rubin. |
