Image guided radiation therapy (IGRT) has become increasingly popular during the past five years, although it was in use for many years before that. IGRT is the delivery of radiation with daily visual guidance. Every patient today undergoes some version of image guidance with once-a-week localization films. In some cases, image guidance is crucial, especially when treatment fields must be as limited as possible due to nearby critical structures, or when the target of radiation might move, as is typically seen with lung cancers that may move while patients are breathing. In these cases, daily image guidance via IGRT may be beneficial.
In standard radiation therapy, the area at risk is targeted and a margin is added around it to allow for changes in the patient’s position and potential movement of the target area. Using IGRT, margins can be minimized, thus sparing normal tissue that does not otherwise need to be treated.
Cleveland Clinic and IGRT
Cleveland Clinic has been at the forefront of IGRT since the late 1990s. Our first devices to incorporate IGRT technology included the Cyberknife and BAT. We were one of the first sites to offer the Cyberknife, which used two X-ray machines 90 degrees apart to help localize lesions and target them with a radiation device mounted to a robotic arm. The IGRT radiation therapist uses BAT’s ultrasound device to locate the prostate and adjust the patient’s position accordingly. This allows for tighter radiation fields, and, in turn, higher doses and sparing of critical structures. With this IGRT device, we have treated prostate cancer patients in less time by giving more radiation per day. The Radiation Therapy Oncology Group is studying this shortened radiation regimen a national trial.
New IGRT Technologies
Recently, we have acquired technologies to keep us at the forefront of image guided radiation therapy, including the Novalis system, cone-beam computerized tomography (CT), the Calypso system and RESTITU.
Novalis is a sophisticated IGRT treatment system that incorporates two versions of image guidance. External fiducials are used to track the patient position and even can be employed to monitor movements like breathing using infrared reflective technologies. In addition, as with the Cyberknife, patient position can be verified precisely by using two X-ray machines 90 degrees apart. Occasionally, metallic markers are placed within the tumor and/or adjacent tissue to assist in localization. The radiation may be delivered using intensity-modulated radiation therapy (IMRT) with miniature leaves. The Novalis system allows for precise localization and dose distributions.
Cone-beam CT uses a mounted CT scanning device on the linear accelerator to aid in patient positioning. After the patient is placed in treatment position, he/she is scanned using cone-beam CT, and this is fused to the planning CT. The patient is then repositioned accordingly to match the position at the time of the planning CT. Because the patient is precisely positioned, the radiation oncologist is able to minimize the margins used in treatment. The cone-beam CT takes very little time and can be used daily before each treatment. Occasionally, IMRT is used to deliver the treatment. In our department, we have two cone-beam CT systems, each designed to treat tumors of different sizes. This technology gives us flexibility to treat a wide variety of tumors.
Cleveland Clinic’s Department of Radiation Oncology is one of the first sites to investigate the Calypso system. Calypso uses an implanted fiducial that generates a radiofrequency signal when activated. The signal is monitored through a detector panel that allows for radiation treatments to pass through. Because the radiofrequency signal is monitored many times per second, the tumor may be tracked during the course of radiation. Some of the research contributions by the Department of Radiation Oncology led to recent U.S. Food and Drug Administration approval of the Calypso system. The role of this device in treatment is being investigated.
We have obtained the RESTITU system for treatment of prostate cancers and other tumors. Like the BAT system, this uses ultrasound to determine the position of various structures, and the patient is shifted accordingly. The RESTITU system has an easy user interface, making this a more efficient process.
Cleveland Clinic is always at the cutting edge of medicine. The Department of Radiation Oncology is making these technologies, like IGRT, available to our patients and will continue evaluating new technologies for the future.
