TBI Using Arc Technology More Comfortable for Patients

BOSTON—A new, intensity modulated radiation therapy delivery system allows patients to lie down rather than stand up for total body irradiation (TBI) and avoid the discomfort of heavy lead shields to block the lungs, John T. Keane, PhD, reported at the American Society for Therapeutic Radiology and Oncology (ASTRO) annual meeting.

Dr. Keane, computer systems manager in the Department of Radiation Oncology, Montefiore Medical Center, Bronx, NY, said that the modified technology, known as intensity modulated arc therapy (IMAT), was initially developed to save space. Conventional total body irradiation with a linear accelerator requires a very large room, he said, with enough distance between the patient and the accelerator to project radiation beams uniformly over the entire body.

Instead of using a gravity-oriented compensator to account for differences in dose distribution, IMAT uses an intensity modulated continuous arc beam pattern.

The patient lies on the floor, part of the time prone and part of the time supine, as a gantry moves the radiation beam above the patient in a pendulum-like swing, or arc beam pattern (see Figure 1). A high-power computer changes the multileaf collimator aperture field sizes dynamically during the treatment.

Dr. Keane and his colleagues concluded that the uniform dose profiles required for total body irradiation treatment could be delivered accurately (see Figure 2) and in a more comfortable way using this method.

In an interview with ONI, Bhadrasain Vikram, MD, chairman of the Department of Radiation Oncology, Montefiore, described the technique as a boon to patients, who often find the lung-shielding lead blocks heavy to wear and sometimes become nauseated during treatment.

"Necessity is the mother of invention," he said. "The traditional technique requires a very large room to treat adult patients. I couldn’t spare such a large room, so I asked the physicists to come up with something we could use in a small room."

The hospital had not been able to do away with the blocks because of the risk to the lungs. "The linear accelerator has a built-in computer, but the computer was not powerful enough," Dr. Vikram said. He expressed confidence that the computer will now be able to reduce radiation when passing over the lung.

Dr. Vikram said the researchers are working with Varian Medical Systems to make the technique commercially available. "Many more hospitals can use this technique," he said, crediting Dr. Keane with developing the software that makes it possible.

IMAT to Specific Organs

In another ASTRO presentation, researchers from the University of Maryland Medical Center, Baltimore, discussed their use of IMAT to deliver radiation therapy to specific organs.

"Other intensity modulated rotational methods require patients to move during treatment and use thinner beams to deliver the radiation," said Cedric Yu, DSc, director of Medical Physics. "IMAT, however, does not require patient movement and uses open beams, which allow more radiation photons to pass through."

In the Maryland study, 25 patients with various types of cancer, including prostate, head and neck, and nasal/pharynx cancer, received therapy for an average of 30 days. Before each procedure, a practice treatment was performed to ensure accuracy. "The results showed that the IMAT method delivers a more uniform, higher concentration of radiation for different sites in the body. Also, patients spend less time, about 7 minutes, on the treatment table." Dr. Yu said.