In use at MD Anderson Proton Therapy Center in Houston, Texas, for more than three years now, intensity modulated proton therapy (IMPT) permits doctors to treat one tiny section of a tumor at a time — even as small as a pixel — by adjusting the proton beam dose, direction and depth to wider and narrower contours of the target, while significantly reducing the amount of unintentional radiation hitting nearby healthy tissue.

 

IMPT pairs the precision of pencil beam scanning with the latest three-dimensional imaging technology to map the exact size, shape, density and location of the tumor, and its proximity to neighboring organs. It’s being deployed at several proton centers around the world.

 

MD Anderson has used IMPT to treat more than 1,500 cancer patients so far. And radiation oncologists there are currently conducting four clinical trials comparing IMPT to intensity modulated radiation therapy (IMRT), the preferred radiation treatment at cancer centers that don’t have access to protons.

 

Steven Frank, M.D., medical director at MD Anderson Proton Therapy Center, is so encouraged by patient results that he anticipates IMPT will eventually replace IMRT as the go-to radiation treatment for most malignant tumors.

 

“Our job is to focus radiation on the tumor and eliminate it from areas it doesn’t need to be,” said Dr. Frank. “With IMPT, you have less radiation going in before the tumor and no radiation coming behind the tumor. IMPT will allow us to treat any cancer we currently treat with IMRT — and curtail the side effects both acutely and long-term.”

 

Dr. Frank first put IMPT to use in 2010 to help a 33-year-old mother of three who other cancer centers had refused to treat. Her tumor was located inside her nasal pharynx and was wrapped around her brainstem. “She came to us,” he recalled. “We couldn’t treat her with IMRT. But this technology, IMPT, allowed us to give her the doses needed to eliminate her disease. Three and a half years later, she has no evidence of disease.”

 

IMPT’s early clinical results are spurring more and more radiation oncologists to install a proton therapy system at their cancer centers.

“The problem is it can’t come fast enough because of cost,” Dr. Frank added. But there, too, advances in technology are helping make proton systems more affordable to more cancer centers in the United States, Europe and Asia, he added.

 

Proton centers built five to 15 years ago required buildings the size of a football field to hold the immense and intricate system that generates the proton beams used for cancer treatment. The system’s 130-ton particle accelerator and beam line are housed within concrete walls that are 9 to 12 feet thick, and strong enough to support 20 floors overhead. Typically, those walls support a 90-ton gantry for each of the treatment rooms.  The gantry permits the proton beam nozzle to rotate almost fully around the patient. The price tag for a proton center with four to five treatment rooms back then was about $150 million to $200 million dollars — a major financial barrier for most cancer centers.

 

But in recent years, proton system makers have dramatically reduced the size of the accelerator and beam line by 60 to 70 percent. And the cost has dropped almost as much for a single treatment room system.

 

“As the footprint becomes smaller and the cost comes down, you’ll see a proliferation of proton therapy,” Dr. Frank said.

 

According to the Proton Therapy Consortium, half of the 26 proton centers currently under construction around the world are single-room proton facilities.