A new "beam shaping" system will allow doctors to zero in on hard-to-reach tumors and bombard them with radiation while sparing the surrounding healthy tissue, its developer says.
The Millennium MLC-120 from Varian, a Palo Alto, California, maker of medical products, shapes a radiation beam to match the form of a cancerous tumor, making the therapy more effective and avoiding damage to other tissue.
The multi-leaf collimator -- which causes radiation beams to move as parallel rays -- uses tiny, overlapping leaves to shape the beam. Varian's new device uses 120 moving leaves, while the standard device today has 80. It works like a camera aperture with mechanical leaves that can be programmed to sculpt the shape of a tumor.
"The whole goal of targeting radiation is so that you’re precisely delivering the radiation exactly where the sick cells are and avoiding the healthy tissue," said Michelle Maynard, delivery systems product manager at Varian. "We've radically improved the targeting in an automated manner."
Not only does the MLC-120 have more leaves, but some measure only half a centimeter, half the size typically found in collimators.
The additional leaves also provide for a larger area of treatment, said Bobby Baker, oncologist and president of the Cancer Institute of Maui. "...In the past, it's been a problem that you couldn't get a large enough field -- up to only 40 centimeters with the 80-leaf collimator."
A new type of radiation delivery called Intensity Modulated Radiotherapy (IMRT) adds a third dimension to the tumor-killing process.
"This is probably the newest revolution in cancer therapy, because if you think about what we were doing, two dimensional process could only get so conformal," Maynard said. "With this process you're able to ... improve your conformality with a level of precision no one's seen before."
By using the new collimator and IMRT together, oncologists can take a three-dimensional computer model and make a beam come out in the shape of the tumor.
"It's almost like using a laser, it's so precise," Maynard said.
The fear of damaging healthy tissue surrounding the tumor has limited the amount of radiation doctors could use to kill a tumor. But doctors at Memorial Sloan-Kettering Cancer Center in New York who tested this technique found that they could increase the amount of radiation per dose with fewer side effects, which improved cancer cure rates.
Without a multi-leaf collimator, radiation oncologists must hand-pour lead blocks to shape the beam of radiation after measuring the tumor, Maynard said. This technique gives extremely smooth edges to the perimeter of the radiation delivered, but is labor intensive. Plus, oncologists typically deliver the radiation from up to 12 different directions and each change requires the technician to walk into the other room and reposition the block. With a collimator, the adjustments are made automatically using a computer.
"Where radiation is indicated these devices are very useful and important. In particular, for sites where critical normal tissues are close to the tumor, these devices could make the difference between long term remission (ie "cure") and failure," said Peter Fessenden, professor of radiation physics at Stanford University in Palo Alto, California.
At the Cancer Institute of Maui, Baker said doctors still employ hand-poured blocks, but he's anxious to try the new technology.
"A multi-leaf collimator will never be as accurate as a hand-made block, but the difference is relatively insignificant," he said. "The biggest advantage is to improve streamlining and efficiency." By some estimates, clinics could increase the number of patients treated by 50 percent with the same staff size.
The MLC-120 will be part of Varian's Generation 6 platform, a database which integrates patient data charts, diagnostic imaging, treatment planning and simulation, treatment verification, and medical records and reporting.
The company expects the Millennium MLC-120, which is already in use in Australia, to receive FDA clearance by March.
