the Promise of the Proton Beam
Shaping the MGH November 1994.
Copyright the Trusteees of Massachusetts General Hospital, 1994
Realizing the promise of the proton beam
challenge of radiation oncology has always been to deliver as much
cancer-killing radiation to a tumor site as possible, while delivering
the smallest possible dose to adjacent healthy areas. Most of the
side-effects of radiation result from its interaction with normal
tissue. If the area exposed to treatment can be reduced, more powerful
radiation beams can be used, which increases the likelihood that
the tumor will be destroyed.
While standard radiation therapy (A) delivers radiation (red
and yellow) to a much larger area than a tumor (white outline),
proton beam radiosurgery (B) concentrates the radiation in a much
smaller area, releasing most of its energy in and directly around
several types of tumors, proton beam therapy allows just such precise
targeting and delivery of high-energy protons to a very limited
area, reducing the radiation dose to normal tissues. For more than
30 years, the MGH has been the world leader in proton beam research
chief of Radiation Oncology Herman D. Suit, MD, PhD, explains that
when the positively-charged atomic particles called protons travel
through tissue, they have a limited range, depending on the power
of the proton beam. As they reach the end of their range, protons
release a burst of energy within a very limited area. Controlling
the power of the beam allows delivery of radiation to the tumor,
but not to tissues lying behind the tumor.
contrast, x-ray beams pass through the entire body, releasing a
steady dose of radiation along the way. Because the area affected
by the proton beam can be carefully controlled, it becomes feasible
to deliver a much higher dose to the tumor itself than can safely
be done with standard x-ray treatments.
the proton beam requires a cyclotron, a machine that accelerates
subatomic particles to nearly the speed of light. The Harvard Cyclotron
Laboratory (HCL), one of the world's first such facilities, was
built in the 1940s for research in nuclear physics. In the early
1960s, researchers from the MGH and the Massachusetts Eye and Ear
Infirmary (MEEI) began working with the HCL staff to treat patients
using proton beam therapy.
Suit explains that, starting in 1961, MGH neurosurgeons William
Sweet, MD , and the late Raymond Kjellberg, MD, used proton
beam therapy on benign tumors of the pituitary gland. One of its
most successful applications has been to destroy or shrink arteriovenous
malformations (AVMs), tangled masses of immature blood vessels in
the brain that can cause serious neurological problems or death.
1974, MGH and MEEI researchers have been investigating the use of
proton beams to treat cancer patients, work that has been supported
by the National Cancer Institute since 1976. Proton beam therapy
has proven more effective than other methods in treating certain
tumors of the eye and the base of the skull. It also is being tested
for patients with several other malignancies -- including tumors
of the brain and spine, the lining of the brain and spinal cord,
and prostate and rectal cancers.
beam allows us to destroy some tumors with a single treatment, says
Chapman, MD , MGH neurosurgeon. 'It really is a non-invasive
form of radiosurgery, compared with standard radiotherapy treatment
that must be done over several weeks.'
the World-War-II-era Harvard cyclotron has some serious limitations.
Its relatively low power means that it can treat only tumors located
close to the body's surface. The beam's position is fixed and cannot
be rotated around a patient, as is possible with standard x-ray
therapy equipment. This fixed location also can make it difficult
or impossible to aim the beam from an angle that might produce the
most effective result.
its maximum capacity, the current facility can treat only 20 patients
a day. In addition, the location and environment of the HCL facility
are far from ideal for patient treatment. The center is located
four miles away from the hospitals, and was originally designed
as a nuclear research facility.
lack of medical and other support services also limits the availability
of certain treatments. For example, the difficulty in providing
anesthesia support on site makes delivering proton beam treatment
to young children cumbersome.
been very difficult to take advantage of the full potential of proton
beam technology in such an old facility,' Dr. Chapman says. 'I compare
it to racing a thoroughbred horse around a pony-cart track. You
just can't get the same results as you would in the appropriate
surmount these limitations, the MGH and other regional academic
medical centers have joined forces to create the Northeast Proton
Therapy Center. The center will be a modern treatment facility on
the MGH campus and will be capable of delivering high-energy, movable
proton beams to virtually any site in the body. When complete, it
will be the only resource for proton beam therapy in the Northeast
and one of only two hospital-based facilities in the country.
treatment rooms with faster, more powerful equipment, will more
than triple the numbers of patients that are able to be treated.
Patient treatment and waiting areas will be much more comfortable
and welcoming, and the on-campus location will provide convenient
access to the hospital's complete medical and support services.
new facility will also have the resources needed for research to
further improve treatment techniques, compare proton beam to advanced
forms of standard radiation therapy, investigate new applications,
and improve the procedure's cost effectiveness.
Constructing the Northeast Proton Radiosurgery Center is an ambitious
undertaking, which should be completed in mid-1998. The National
Cancer Institute has committed $6 million for planning and development
and $20 million for construction and equipment. An additional $20
million must be raised by the MGH and other participating institutions.
far as we're concerned,' Dr. Suit says, 'prospects for further improvement
and expanded uses of proton beam threapy are certain. The only question
is how big those gains will be.'
the Northeast Proton Radiosurgery Center will help bring promising
new treatment options to thousands of cancer patients from around
be built on the MGH campus, the Northeast Proton Radiosurgery Center
will have three treatment rooms with movable proton beams, more
than tripling the number of patients that can be treated currently.
Patients will receive therapy in a more comfortable environment
than is possible in the current facility, which is more than 45