Hitting the Target: IMRT & IGRT Pinpoint Cancer Therapy

Twitter icon
Facebook icon
LinkedIn icon
e-mail icon
Google icon

Elekta's Synergy IMRT systemIntensity modulated radiation therapy (IMRT) has moved from experimental to becoming the standard of care in record time. And, physicians are treating more and more cancers with the process all the time.

Single vendor, complex process

Indications for IMRT are growing, says James Rembert, MD, radiation oncologist at Alta Bates Summit Comprehensive Cancer Center in Berkeley, Calif. About one-third of the center’s patients get IMRT, he says. The facility implemented IMRT equipment from Varian in 2001. A big reason for selecting Varian, physicist Ronnie Chen says, was that the center already was a Varian customer. “There is always an advantage in using the equipment of a single vendor. IMRT is a very complex process,” Chen says. Working with one vendor means all the components are designed to work together seamlessly. If there is a problem, there is only one vendor required rather than having to spend time tracking down different vendors for each component.

Alta Bates had the equipment installed and ready to use in about eight weeks. “When we implemented IMRT, it was a relatively new procedure,” says Chen. The radiation oncologist at the time educated referring physicians about IMRT, how it worked and expected results. “We started up with prostate IMRT and once we got experience with that, we started applying IMRT to head and neck cases, and eventually to the brain and other parts of the body.”

“As we get better about figuring out exactly what regions are at risk, the indications for IMRT are growing and growing,” says Rembert, who has started using IMRT to treat rectal cancer. The treatment actually is affecting the natural history of head and neck cancers, too, he says. “In the past, it was hard to get the dose you needed to cure cancer without destroying critical structures. With IMRT, you can get that extra dose and spare normal tissues. We tend to achieve local control in greater than 85 percent of patients.” Now, Rembert and his colleagues have patients presenting with metastatic cancer down the road. Previously, they would have died from local disease before it could metastasize.

The growing use of IMRT has necessitated better image guidance. For example, prostate cancer patients can be implanted with seeds that the technologist can track and use to line up treatment. “That allows us to be very accurate,” says Rembert. And, the linear accelerator is equipped to generate a CT scan without the patient in the treatment scan. “We can be accurate within a millimeter or so.”

Since IMRT is still relatively new, only recently have physicians coming out of residency emerged with a familiarity with the procedure. Because of the level of complexity level and costs, it will take time for the majority of facilities and practices to offer the treatment. “You need a linear accelerator with a certain baseline of features and equipment installed on it and older centers probably don’t have that,” says Rembert. Training includes learning which cases are appropriate for IMRT. “Make sure that what you use it for really requires it,” says Chen. “Some people are using it for inappropriate reasons. The use of IMRT should be dictated by medical necessity.”

Therapists need to be aware that IMRT is a complicated procedure, Chen adds. “If you don’t align the patient properly, you can miss the target. The dose gradient in an IMRT treatment plan is very steep so therapists need to know the importance of proper setup.” Many practitioners are using image-guided technology to localize the target and ensure proper IMRT delivery. That offers safety measures but the equipment is still operator-dependent, says Chen. ”The machine can help you localize the target, but it can’t do it for you. The operator still has to use the information provided by the machine to align the radiation beam to the target.”

IGRT: Tighter targets

Todd Barnett, MD, radiation oncologist at Swedish Medical Center in Seattle, agrees that appropriate use is an important consideration. He cautions that a lot of patients don’t need IMRT. “This is going to be evolving to the standard of care, but it’s not necessary for everybody. A simpler approach can be better and just as effective.”

But, when Barnett was in medical school, IMRT wasn’t even imagined and image-guided radiation therapy (IGRT) didn’t exist. Now, the CT scans that can be taken with the newest linear accelerators are better than the CT scan you could get from a scanner in 1993, he says. They also offer the ability to