IMRT

IMRT: Second Helpings

Surpassing 10 years in action, intensity-modulated radiation therapy is enjoying another round of heightened demand. What’s renewing the hunger?

Every successful new technology has its tipping point—the moment at which it ceases being an unknown, little-used device and becomes a must-have tool. Intensity-modulated radiation therapy (IMRT), however, may have had two such points.

The first was likely in 2001, when reimbursement rates for procedures using IMRT soared to four times that of conventional radiation treatment. But its second, quieter "tipping" is going on now, as physicians realize its potential.

After the financial benefits of IMRT became clear, its use jumped. Between 2002 and 2004, utilization among radiation oncologists skyrocketed from 32 to 73 percent, according to a survey of 450 physicians by Arno Mundt, MD, radiation oncologist at the University of Chicago and medical director for radiation oncology at the University of Illinois at Chicago.

"In 2002, hospitals were getting IMRT to overcome the guy down the street," says Dr. Mundt. "Later, they were doing it to keep up with the guy down the street."

As IMRT gets into more and more hands, though, experience is changing expectations. Rather than simply doing the same old procedures better, physicians are now doing different procedures altogether and thinking about those procedures with refocused vision.

"IMRT is still a work in progress," says Dr. Mundt. "Now that people have been working with it for a while, they are starting to realize all the things that might be done with it."

The difference between IMRT and traditional radiation therapy is in the "M"—modulated. IMRT uses the same medical linear accelerators employed in conventional therapy, but it also uses dynamic multileaf collimators (DMLCs) to shape the radiation beam to the tumor. DMLCs employ dozens of movable metal "leaves" to screen and protect healthy tissue.

"In the beginning, most physicians looked at IMRT as just an improved version of conventional therapy," says Dr. Mundt. But now that the technology has surpassed its 10-year mark—with thousands of patients treated—physicians are getting bolder.

At the Dale and Frances Hughes Cancer Center in East Stroudsburg, Pa., for instance, IMRT was initially used for prostate and breast cancers. After refining its expertise there, however, the center began treating tumors of the head, neck and brain—locations whose numerous critical structures make physicians proceed much more slowly.

"IMRT allows us to be more accurate in our treatment," says Michael Greenberg, MD, medical director, whose center has used the technology since early 2000. "And it has almost zero side effects."

Cindy Sharfen, MD, agrees. Previously, treatment of head and neck cancers tended to damage salivary glands, resulting in chronic dry mouth, says the oncologist at the Redwood Medical Group, Ukiah, Calif.

"Patients always walked around with a water bottle," says Dr. Sharfen, "but now we see patients with near-normal salivation. That equals a huge difference in their quality of life."

However, despite IMRT’s significant benefits, some clinicians question whether additional treatment fields could produce second malignancies. That’s because traditional therapy radiates a tumor from only one or two directions, while IMRT’s ability to shape the radiation beam requires oncologists to treat it from posterior, anterior and side vantages. In this scenario, the tumor may receive radiation from six, seven or more directions. "They are low doses," says Dr. Greenberg, "but they are more spread out." Still, he says, IMRT has been used in clinical settings for more than 10 years with no evidence that healthy tissue is suffering.

According to Richard Stark, director of delivery systems for Varian Medical Systems, Varian’s "sliding windows" technology for delivering IMRT enables clinicians to use the fewest possible number of treatment beams and still obtain the desired dose conformality.

The cost of using IMRT varies with the location of a tumor, the equipment setup of a particular facility and the training of the clinicians. Joseph Ting, PhD, chief medical physicist at Melbourne (Fla.) Cancer Center, has seen the process take hours, and he has seen it take minutes.

At his facility—equipped throughout by Varian—"a prostate is typically a half hour planning period," says Dr. Ting. "Head and neck planning takes two or three hours."

In the latter case, however, planning can take much longer if data from one company’s technology must be transferred to another’s.

"User training is also a huge issue," he says. "All the vendors offer training, but it’s like driver’s ed: You learn the most about driving by driving."

One thing is clear: IMRT has become the standard of care for many types of cancer at treatment centers around the world. The proof is in the purchasing: For Varian, 95 percent of linear accelerators ordered in 2004 included IMRT capabilities. And with image-guidance technologies on the way, IMRT stands poised to take another leap in applicability. Image-guided IMRT will enable clinicians to use IMRT in areas of the body where tumors move around, either due to respiration or other physiological processes.

October 2005

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