Pencil beam scanning technology, an even more advanced and targeted form of radiation treatment known as proton therapy, is now being used to treat patients with lung cancer at The University of Texas MD Anderson Cancer Center.
Proton therapy derives its advantage over conventional forms of radiation from its ability to deliver radiation doses to a targeted tumor with incredible precision that avoids surrounding tissue. This results in fewer side effects during and after treatment, and greater tumor control. Most proton patients are treated with a technique known as passive scattering, which uses apertures to shape the proton beam and deliver a uniform dose to the tumor.
Pencil beam scanning proton therapy delivers a single, narrow proton beam (which may be less than a millimeter in diameter) that is magnetically swept across the tumor, depositing radiation like a painter's brush, without the need to construct beam-shaping devices. This technology continues to build on the patient benefits already offered with proton therapy – more targeted, higher tumor dose, shorter treatment times, reduced side effects and increased treatment options.
"The advantage lies in the beam's capacity to approach the tumor from multiple directions, creating a "U" shape around these structures and avoiding them entirely during treatment," said James D. Cox, M.D., professor and head of the Division of Radiation Oncology at MD Anderson. "Pencil beam is more like a very fine airbrush. Instead of needing a brass template to define the shape, the proton beam is made ultra fine to conform to the contours and landscapes of the tumor."
MD Anderson's Proton Therapy Center, which began treating patients in May of 2006, is the first in North America and only one of three clinical centers in the world to treat patients with pencil beam scanning technology. Additionally, MD Anderson is the first center in the world to treat lung cancer patients using pencil beam scanning proton therapy.
"The unique part about lung cancer is that it's close to the esophagus, aorta and spinal cord, and all of these critical structures are important for the body to function," said Joe Chang, M.D., Ph.D., associate professor in MD Anderson's Department of Radiation Oncology. "The proton beam provides much more conformal radiation, which means higher doses to tumors and lower dosages to critical structures nearby."
Another benefit of pencil beam scanning proton therapy is its use in patients with recurrent disease, who have already received full doses of radiation, Chang said. In this case, pencil beam limits or eliminates radiation to these sensitive areas.
As the therapy advances, one of the next steps is using imaging tools to predict the movement of tumors, both lung and other cancers, to offer even greater precision.
"Four dimensional imaging and treatment planning help us to know how much the lung or tumor moves, so we can adapt the pencil beam," Chang said. "Now, with new technology, we know the pattern of this motion."
According to the American Cancer Society, an estimated 222,520 new cases of lung cancer will be diagnosed in 2010. Despite advances, the long-term survival rates of lung cancer remain low, reinforcing the need to expand therapies that offer a greater combination of potency and accuracy.
Billy Walls, 75, from El Paso, Texas, was the first lung cancer patient to be treated with pencil beam technology at MD Anderson. Originally diagnosed in 2004, Walls underwent a partial surgical resection of his lung, along with chemotherapy and radiation. Four years later, his cancer returned to the same location and he was advised against further surgery and told about proton therapy.
"Hope is the main benefit," Walls said of his pencil beam experience. "I don't feel anything during treatment, I haven't lost any weight, I'm not coughing as much, and I still walk in the mornings."
MD Anderson Proton Therapy