Hitting the Target: IMRT & IGRT Pinpoint Cancer Therapy

Intensity 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 see the target every day or in real time and to more accurately place the fields. Rather than using marks on the body or an x-ray to track the target, the IGRT capabilities of Elekta’s Synergy system allows the technologist to take a CT scan right on the table while the patient is in the treatment position.

“You can see exactly where the prostate is and compare where it is today to the treatment plan and make adjustments,” Barnett says. “That allows you to keep your fields smaller and tighter,” exposing less normal tissue to radiation. “Because of the uncertainty before, we had to make the fields bigger so we wouldn’t miss and that would cover more normal tissue.” Real-time tracking ability means the machine can turn off and on quickly as the tumor comes into the treatment window. “If the tumor is moving up and down, the machine can pulse on under the beam and not treat too big of an area.”

Barnett says his facility went with Elekta because “we felt that Elekta was a little bit ahead of the curve. We were very comfortable that the Elekta equipment would work with the software we already had substantially invested in, allowing us to get the full functionality, all the bells and whistles.”

Barnett has been treating lung cancer patients, most of whom are not healthy enough to receive much radiation or undergo surgery. Because he can give a higher dose of radiation to a higher volume of the tumor, “patients seem to be doing better and tolerating treatment well. These are patients we wouldn’t have treated before.”


‘Our dream come true’

Hansen Chen, physicist at Christiana Care Healthcare in Newark, Del., uses Siemens IMRT equipment because it offers the “step-and-shoot” method of treatment delivery. “We were more comfortable with that because it’s more stable. It’s static versus dynamic and static is more like the old way of delivering radiation. Psychologically, you don’t feel a big change and you can verify in each segment before you deliver the radiation.”

IMRT adds more steps to treatment, says Chen. The treatment planning stage is significant because of all the pixilation the computer needs to do. Also, the contouring process takes time because “you really have to define where to hit and where to avoid.” Once treatment is underway, the physicist has to do quality assurance — measuring to see if each treatment session matches data from the treatment plan system. “It’s complicated delivery so we have to be careful and do QA on every patient plan.” The latest advances have reduced QA time, Chen says, by using the imaging device for verification.

Having been a physicist for 12 years, Chen says IMRT “is our dream come true.” And, “the next step is happening now.” Where IMRT is the treatment delivery method, IGRT is the insurance that what you’re delivering with IMRT is true. “When we are doing the treatment plan on the computer, we are kind of assimilating the patient,” says Chen. In reality, the patient can be anywhere depending on how they are set up that day. “There is some uncertainty. IGRT makes sure that what you plan is what you’re going to get on the patient.”

As radiation oncologists learn more about IMRT and IGRT, there is no doubt that indications will continue to increase along with demand. “It’s an incredibly exciting time to be a radiation oncologist,” says Rembert. “This is more sophisticated and better for patients. It is a way for us to improve our therapeutic index — improve treatment but decrease side effects.”