[ RadSafe ] Article: Is the Future Bright for Proton Therapy?
crispy_bird at yahoo.com
Mon Oct 1 21:54:31 CDT 2007
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Is the Future Bright for Proton Therapy?
Despite the promise it's shown, proton beam therapy is
only available at a handful of U.S. facilities. Will
it become a key component of cancer treatment?
By Mark McGraw
This past January, the University of Florida Proton
Therapy Institute (UFPTI) performed its 1,000th proton
therapy treatmentâless than six months after opening
its doors to patients. The milestone came just days
after the Jacksonville, Fla.-based facility opened a
second treatment room, which effectively doubled
patient volume. The Loma Linda ( Calif. ) University
Medical Center 's James Slater Proton Treatment Center
has successfully treated more than 12,000 patients
since opening its doors in 1990.
Proton beam radiation therapy essentially operates on
the same principle as conventional radiotherapy
--ostensibly killing cancerous cells and preventing
them from replicating. Proton therapy works by aiming
energetic ionizing particles at a targeted tumor. As
protons scatter less easily in the tissue, there is
very little dispersion, and the beam remains focused
on the tumor shape without causing much damage to
The treatment has shown positive results in treating
various types of cancer -- pediatric cancers, brain
and spinal tumors, prostate, lung, head and neck
cancer, malignant melanomas -- while reducing some of
the side effects commonly associated with
radiotherapy. While conventional radiation therapy
remains a proven and often preferred form of
treatment, proton therapy holds great potential, says
James D. Cox, MD, head of the division of radiation
oncology at M. D. Anderson Proton Therapy Center .
But the M. D. Anderson proton center, UFPTI and the
Loma Linda center are three of just five facilities
currently providing proton therapy cancer treatment in
the United States .
Despite its promise, the cost and logistics required
to start and maintain a proton therapy facility have
prevented the treatment from becoming commonplace. But
proton therapy's development steadily continues, as
existing centers are successfully treating patients by
the thousands, and plans for additional, world-class
facilities are being put in motion.
The University of Pennsylvania, for example, is slated
to open a proton therapy institute in 2009. Hampton
(Va.) University has received approval to begin
construction on the Hampton University Proton Beam
Therapy Center , and a facility at Northern Illinois
University that has gained the support of some of the
state's political heavy hitters will start seeing
patients in 2011.
Stopping on a dime
The idea that proton treatment could be effective in
fighting cancer isn't exactly a new one. Robert R.
Wilson, the physicist generally considered "the father
of proton therapy," first suggested as much in a paper
published in 1946, when he was involved in the design
of the Harvard Cyclotron Laboratory (HCL).
The first treatments were performed at particle
accelerators built for physics research, such as
Berkeley Radiation Laboratory in 1954. A collaboration
between HCL and Massachusetts General Hospital in
Boston to pursue proton therapy began in 1961. That
program treated more than 9,000 patients before the
Cyclotron was shut down in 2002. Overall, more than
55,000 patients around the world have been treated
with proton therapy, and between 15,000 and 17,000
have been treated exclusively in the United States for
some 50 different types of tumors, according to the
National Association for Proton Therapy.
Still, proton therapy has largely been used for
research purposes, says Dr. Cox. The Loma Linda
center, which was recently renamed to honor its
founder, became the world's first clinically-based
proton facility a mere 17 years ago. The M. D.
Anderson proton center is just the fourth of its kind;
the only proton therapy facility in the Southwest.
M. D. Anderson, one of the world's most renowned
comprehensive cancer centers, opened its
94,000-square-foot proton therapy center in May 2006.
The center now treats an average of 55 to 60 patients
on a daily basis, Dr. Cox says. The most precise form
of radiation treatment for some tumors, proton therapy
has the same biological effect as an X-ray, he adds.
The difference is the radiation dose distribution.
Protons are heavily charged particles that "deposit
energy [in the body] very differently" compared to an
X-ray, Dr. Cox says. In proton treatment, the dose is
much lower upon entering the body, he adds, and the
major dose distribution occurs when the proton comes
to a stop. Protons have a very low dose of energy when
entering the body, and no dose as they exit.
The way protons distribute energy is comparable to
that of a firecracker going off at the site of the
tumor, says Stuart Klein, executive director of UFPTI.
The effect is different in standard radiation therapy,
which he likened to a bullet going through one side of
the body and coming out the other. The ability to stop
protons "on a dime" without disturbing surrounding
tissue is the key advantage of proton therapy, he
The point where the proton comes to a halt is
determined by how much energy it is given, Dr. Cox
says. At M. D. Anderson and Loma Linda, for example, a
compact particle accelerator known as a synchrotron
accelerates protons to variable energies into the beam
transport line. The synchrotron contains magnets that
confine the protons so they travel in a set path
through a vacuum chamber. During each revolution
through the chamber, protons gain an increment in
energy from radiofrequency power. After many cycles,
the protons reach the energy required by a treatment
plan and are extracted into the beam transport line,
which then directs the proton beam to the patient in a
In the process, "we can focus [proton treatment] and
shape it, so we can make the high-dose area in the
body correspond to the shape and size of the tumor,"
Dr. Cox says. "That's something we can't do with
A weighty issue
As noted, the costly technology and large space
necessary to house it has contributed to keeping
proton treatment from becoming more common in the
At the two-story M. D. Anderson proton center, for
example, there is one fixed-beam treatment room, an
experimental treatment area, a range of patient and
research support areas, a synchrotron, beam transport
system and three gantry treatment rooms. Gantry
patient treatment rooms have a patient treatment bed
framed by a large wheel known as a gantry. The
gantries here, which rotate around the patient to
direct the proton beam at its target, are 35 feet in
diameter and weigh about 200 tons, about the same as a
Boeing 757 aircraft.
At UFPTI, each gantry room is three stories high, and
each gantry weighs about 200,000 pounds, says Klein.
The facility is equipped with a cyclotron, a 440,000
pound accelerator that speeds the protons to the
desired energy, ranging from 230 MeV to 250 MeV. Once
protons reach the optimal speed, magnets are used to
direct the protons into a beam line that carries the
protons into treatment rooms.
The equipment in use at UFPTI is comparable to that
found at the Francis H. Burr Proton Therapy Center in
Boston , Klein says. Two of the treatment rooms at the
Burr center, located on the main hospital campus of
Massachusetts General, incorporate 110-ton gantries
that can be rotated to aim the proton beam from
various directions. Patients in gantry rooms lie on
robotic beds which can be adjusted for exact alignment
of targets contained throughout the body.
The sheer size of proton therapy equipment, however,
and the considerable expense attached to a proton
facility doesn't figure to decrease anytime soon,
which will likely limit the treatment to select
centers for the foreseeable future, he predicted.
"[Proton therapy] will continue to be more of a
regional resource," Klein says, "as opposed to being
located at every community cancer center. You'll never
see a proton therapy facility on every street corner."
Nevertheless, Dr. Cox is optimistic that proton
treatment will be proven as a viable alternative -- or
complement -- to conventional radiotherapy in treating
The precision with which proton therapy allows
physicians to focus treatment and administer higher
doses while still seeing reduced side effects bodes
well for proton therapy's continuing development, he
"I really do think proton therapy is the wave of the
future," Dr. Cox continues, adding that he believes it
will become much more widely used as technology is
further developed and refined, which will help in
driving cost down.
Recent improvements in diagnostic technology, such as
high-resolution MRI and CT scanners, allow physicians
to more accurately visualize the exact shape, size and
depth of tumors, Klein notes. The exact knowledge of
the three-dimensional aspects of the tumor has
advanced the applicability of proton therapy.
A wide range of patients stand to gain from the
treatment; patients that should be carefully selected
based on the criteria that their tumor needs a high
dose and is close to sensitive organs, Dr. Cox says.
Such decisions are made by an accomplished team of
radiation oncologists at the relatively new M. D.
Anderson proton facility, which is treating patients
10 hours a day despite not being at full capacity just
yet, he adds.
Proton therapy facilities such as M. D. Anderson,
UFPTI and Francis Burr are also home to research
programs that are investigating new disease sites that
may benefit from the therapy, and searching for ways
to improve current treatment techniques and equipment.
The ultimate aim of such efforts is to prove proton
therapy's efficacy, "to be able to demonstrate the
much more widespread applicability and advantage of
this kind of treatment," Dr. Cox says, "and combine it
with the other disciplines that are involved in cancer
Mark McGraw is an associate editor at ADVANCE. He can
be reached at mmcgraw at merion.com.
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John Jacobus, MS
Certified Health Physicist
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