Tucked in a corner of the MedStar Georgetown University Hospital campus in Washington is the country's 28th proton therapy center, which is set to begin treating patients in March. This small but state-of-the-art system is designed to attack tumors more quickly than its predecessors in proton therapy, a type of radiation treatment that spares healthy tissue.
Patients have been treated with protons since the 1950s. But since the first hospital-based treatment center opened in California in 1990, the pricey technology has grown in popularity.
Only four proton therapy centers existed nationwide a decade ago, according to the National Association for Proton Therapy. With 24 under construction or in development, the total may soon exceed 50. A center at D.C.'s Sibley Memorial Hospital is scheduled to open in late 2019, and the Inova Schar Cancer Institute in Fairfax, Virginia plans to open one by 2020. The Maryland Proton Treatment Center, affiliated with the University of Maryland, was the area's first, opening in Baltimore in 2015.
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All types of radiation treatments break the DNA in cells, which makes it harder for them to multiply. Rapidly dividing cancer cells are particularly susceptible to this kind of damage, so tumors often shrink or disappear.
The difference between traditional radiation and proton therapy is in how the radiation is delivered.
Traditional therapy irradiates tumors with X-ray waves, and all tissue along the beams' path gets a similar dose of radiation.
Proton therapy instead uses beams of protons, charged subatomic particles that can be controlled with magnets. A small amount of radiation is deposited on the way into the body, most of it goes directly into the tumor, and none passes through the other side.
That means, for instance, that radiation aimed at a tumor in one side of the brain wouldn't harm the healthy side. And a beam aimed at a spinal tumor wouldn't reach the heart or lungs.
"You can deliver a high dose to where you need it and spare normal tissues with fewer side effects," said Anatoly Dritschilo, chairman of radiation oncology at MedStar Georgetown.
Because more radiation reaches the tumor, a smaller overall dose is required.
The compact system at MedStar Georgetown spins protons in an accelerator called a cyclotron and releases them when they reach two-thirds the speed of light. This circular system takes up much less space than many other proton accelerators, which propel protons through long, linear pathways at facilities the size of football fields.
Once the protons reach top speed, they pass through a device that uses adjustable plates to focus the beam and shape it to the contours of the tumor. This is a refined version of "pencil-beam" technology, an innovation that came about roughly a decade ago. Before then, proton therapy scattered protons like water from a fire hydrant, Dritschilo said. Now, the beam is more like an easy-to-aim hose.
The beam enters the patient in pulses, irradiating the tumor layer by layer, much as a 3-D printer operates.
Patients must hold still for only seconds at a time, compared with minutes for traditional radiation and older versions of proton therapy.
An entire treatment takes just a couple of minutes (plus about 20 minutes to set up the machine). As with other types of radiation, patients go for treatment once a day, five days a week, for five to eight weeks.
Children who have cancer may benefit most from proton therapy because more of their normal cells are developing rapidly, making them more prone to damage that could stunt the growth of healthy organs, Dritschilo said.
Other main beneficiaries would be people with tumors in the head, neck and spine, and those who have cancers near other very sensitive organs, such as the left breast, which is directly over the heart. For others, choosing proton treatment could be a quality-of-life issue, as in the case of a person whose lungs would be so damaged by extra radiation that they would need to use an oxygen tank.
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For some cancers, less precision is better. Lymphoma treatment, for instance, often requires a wider radius around lymph nodes because of the way the cancer grows and spreads, Dritschilo said. And systemic cancers such as leukemia could not be treated by proton therapy alone.
Many common cancers fall into a gray area, where doctors and patients need to weigh risks, costs and benefits of different types of treatment.
Proton therapy has been controversial when used routinely to treat some types of cancer, notably prostate cancer, because data comparing patient outcomes with other treatment forms is slim and because it is much more expensive than traditional radiation.
Soon, both those issues may begin to be resolved, said Brian Kavanagh, chairman of the American Society for Radiation Oncology. Several large clinical trials comparing treatment methods should yield solid data in the next couple of years. And, as with all technology that has been around awhile, the cost of proton therapy centers is coming down, and the cost to patients should decline as well.
MedStar Georgetown said its small center, which has one treatment bay, cost $39.7 million, including the building. Sibley said its four-bay center will cost at least $157 million, well below the $200 million to $250 million that earlier facilities have cost. Kavanagh said he expects that tech innovations may cut costs by half in the next five or six years.
Meanwhile, he said, other emerging radiation technologies may prove to be equally precise in some cases. These would give doctors more cancer-fighting weapons and patients more choices.
"Competition is a good thing," Kavanagh said. "The pressure to improve other forms of radiation treatment technology in recent years has led to tremendous innovation all around."