From Shaping the MGH November 1994.
Copyright the Trusteees of Massachusetts General Hospital, 1994
Realizing the promise of the proton beam

The 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 the tumor.

For 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 and treatment.

MGH 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.

In 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.

Producing 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.

Dr. 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.

Since 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.

'Proton beam allows us to destroy some tumors with a single treatment, says Paul 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.'

But 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.

At 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.

The 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.

'It's 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 setting.'

To 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.

Three 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.

The 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.

'As 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.'

Supporting the Northeast Proton Radiosurgery Center will help bring promising new treatment options to thousands of cancer patients from around the world.

To 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 years old.

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