Health Imaging & IT - October 2007 - (Page 31) 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.” HealthImaging.com All Trilogy machines from Varian Medical Systems are equipped with an On-Board Imager. Two of the facilities using the system include the University of California at San Diego and the Emory Winship Cancer Institute in Atlanta. To make those adjustments, the OnBoard 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.” Respi- ratory 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. teaching others 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 Health Imaging & IT | O C T O B E R 2 0 07 31 http://HealthImaging.com
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