Intensity modulated radiation therapy (IMRT) continues to gain popularity and now more facilities are turning to image-guided radiation therapy (IGRT) for even more precise treatment of several forms of cancer. Even as the two technologies are the on the leading edge for cancer treatment, further developments are underway. In the near future, adaptive treatment will let radiation oncologists adjust treatment on a daily basis, if necessary.
“IMRT has certainly stayed its course and proven itself,” says Arno Mundt, MD, professor and chairman of the radiation and oncology department at the University of California at San Diego. “IGRT is the new kid on the block. It’s the rave of a lot of vendors.”
These new technologies take advantage of a broad range of expertise, says Todd Pawlicki, PhD, medical physicist and Mundt’s colleague. IMRT and IGRT “will allow us to treat some tumors in a way we were never able to treat before—much more accurately, conformally, and with higher doses to the target while still sparing normal tissue nearby. It’s a quantum step. It’s transforming the whole field.”
The team uses a Trilogy linear accelerator from Varian Medical Systems. In-room imaging, using a range of sophisticated technologies, is becoming more and more popular, Mundt says. Plain x-ray films through mounted imagers on the machine guide clinicians, sometimes even during treatment. “Pre-IGRT, we were only able to verify a patient’s position on a weekly basis,” says Pawlicki. “Now, with IGRT for localization, we’re able to actually localize and verify the patient’s position and adjust daily, if necessary.”
Current efforts will lead to real-time adaptive therapy—“the pinnacle for individualized medicine,” says Pawlicki. Adaptive treatment is one of the most important new developments, says Mundt. By imaging the tumor every day to see any changes, clinicians can adapt their treatment efforts accordingly. “That’s a very cutting-edge concept that still needs to be worked out. That’s going to be a paradigm shift in how we treat patients.”
A researcher working with Mundt is looking at adaptive treatment for gynecological tumors. Cervical tumors shrink very rapidly when treated and the uterus can be in a different position every day so gynecological tumors’ response to adaptive treatment is of particular interest. Although adaptive treatment is strictly a research endeavor at this point, Mundt hopes to see it come into practice use within the next couple of years. “We can taste it,” he says.
Increased use of IMRT and IGRT requires “education, education, education,” says Pawlicki. “As a general goal, we need to raise the level of understanding of these technologies throughout the field and how to complement them correctly.” An experience base and an understanding of how to implement accurately and safely is a challenge for the field, Pawlicki says.
More routine offering
Jerome Landry, MD, radiation oncologist at Emory Winship Cancer Institute in Atlanta, Ga., is another early adopter of IGRT technology, having worked with it for about four years. He uses both the Clinic and Trilogy linear accelerators from Varian Medical Systems, equipped with the On-Board Imager for IGRT. “When we began, there wasn’t a lot of clinical experience throughout the country.” Although Landry was originally using the technology in a research mode, he has since used it for pancreatic, prostate and gastrointestinal cancers, and head, neck and brain tumors. “As people started publishing on the side effects, we started offering it more routinely.”
At first, integrating IGRT into the treatment paradigm added an extra 15 to 20 minutes to a 30-minute patient time slot. Once IGRT was integrated for daily set up tracking, Landry worked on clinical efficiency. At first, both therapists and clinicians were at the treatment console and were aligning the patients, using manual matching. The doctors wanted to see all the patients and all of the daily changes the therapists made. They got to a point where they could calculate the average maximum shifts during treatment and gave the therapists parameters. If the shift was less than a certain amount for a certain type of tumor, they could make the shift without referring to the doctor. That extra 15 to 20 minutes was eventually cut down to just four minutes.
Landry recommends increasing the physicist staff during the initial IMRT learning curve. “It’s such a big difference in treatment that it could take an hour to plan one patient.” IGRT didn’t require additional staff and Landry and his team were able to get more efficient fairly quickly.
“I think the potential advantages are enormous,” says Landry. Pancreatic cancers, bowel duct cancers and rectal cancers can receive greater doses of radiation while critical surrounding tissues receive less radiation. “IMRT is great for that. But with IGRT, we can actually track the position of the tumor daily. The theory is that we may not just be giving the tumor more dose, but we are hitting the tumor accurately every day.” Landry has tracked target accuracy when the patient is resimulated weekly versus daily. With weekly simulation, Landry would have hit the target just 30 percent of the time. “It’s a big deal if the tumor shrinks. You have to make adjustments.”
To make those adjustments, the On-Board Imager is mounted on the treatment machine via robotically controlled arms which operate along three axes of motion, so that they can be positioned for the best view of the tumor. An amorphous silicon flat-panel x-ray image detector takes digital images of internal anatomic landmarks.
Both of the accelerators, equipped with the On-Board Imager, combine low-dose, high-resolution kV x-ray imaging and integrated software control of all treatment parameters. These developments allow for extracranial stereotactic radiosurgery, Landry says. The liver moves with respiration, for example, so gating integrated with on-board imaging can monitor a patient’s breathing. “We can localize treatment, plan during breathing and determine which phase of the respiratory cycle has less movement of the tumor and critical structures.” Respiratory motion can be synchronized with the CT image acquisition. The system automatically gates the radiation beam on only when the tumor falls within the planned treatment field.
The Swedish Cancer Institute in Seattle, Wash., installed IGRT from Elekta three years ago. IMRT and IGRT go hand in hand, says Vivek Mehta, MD, director of the Center for Advanced Targeted Radiotherapies at Swedish. “A lot of people think we should never have been doing IMRT before we had IGRT,” says Mehta. “What good is it to be so precise only to be in the wrong spot? IMRT is really a plan—hypothetical directions. If you start at the wrong intersection, you can follow all of the directions and still wind up in the wrong spot.”
Thanks to the facility’s experience with IGRT, they advise others on how to use the technology for the greatest impact on patient care. “These new technologies consume a lot of resources. We can show people how to bring IGRT into their clinic and use it in a resource-efficient manner,” Mehta says. He and his team have a long track record of bringing doctors in from across the country who want to learn in a practical, hands-on approach. “People hear about promise but they really want to talk to someone who’s used it, find out whether it will work in their situation and what we have learned to make it an effective solution.”
Understanding daily changes
William Russell, MD, medical director of the Baton Rouge General Radiation Oncology Center in Baton Rouge, La., has been using IGRT with ultrasound technology for five years. “We have progressed to using IGRT with megavoltage cone beam technology” from Siemens Medical Solutions, he says.
“The ‘holy grail’ of radiation oncology is to destroy cancer without any destruction of normal tissue. For structures with very defined borders, IMRT really added a lot,” Russell says. “IMRT allowed us to treat unusually shaped objects. Instead of treating a tennis ball, we could treat just the shell of a tennis ball. It gave us opportunities to sculpt and shape dose. That’s the real appeal of IMRT.”
The ability to target and understand daily changes with cone beam technology has greatly moved radiation oncology forward, says Russell. “It has changed our ability to apply this technology.” However, there starts to become other issues such as not interfraction, but intrafraction. “If you take a long time to go through the process of targeted treatment delivery, you’ve still lost your advantage. Between the time when you started and ended, you may have lost your target.”
Russell says that plenty of researchers have demonstrated that targets deform with normal organ function and breathing. The challenge that came along with IG-IMRT is to deliver treatment very quickly. “I’m very pleased with megavoltage cone beam technology. We can accomplish fairly complicated treatments in less than 10 minutes. Time becomes more and more important in sophisticated delivery mechanisms.” Now, in a matter of minutes, Russell can acquire a complete 3D structure. “This is very elegant software to match the planned target with the perceived target at the time of treatment. It’s IMRT on steroids, but it’s a very simple system to use. We really can achieve a lot of patient comfort and accuracy and minimal target motion during treatment itself.”
In the future…
IG-IMRT is still the future for 90 percent of the clinics out there, says Mehta. Next up is learning how to track changes and predict changes before they happen to a tumor, and then adapt the radiotherapy plan to be even more precise.
Mundt, who works with Varian on developing new technologies, says that Varian is going to announce major new features at the American Society for Therapeutic Radiology and Oncology’s Annual Meeting in Los Angeles late this month. The changes, including imaging and delivery features, will be “really revolutionary,” he says. “This is really going to change a lot in how we treat patients. It’s really exciting.”
Meanwhile, as physicians become comfortable with this and see the power of this technology, they will use it more and more often, says Russell. Broadband capability is going to allow much more seamless integration of multiclinic sites, he says. “I think that as the application of these technologies becomes more user-friendly that it is going to disseminate very rapidly through radiation oncology facilities in this country.”