Image guided radiation therapy (IGRT) involves the use of imaging technology such as X-ray, ultrasound, or optical imaging to direct the delivery of radiation during radiation therapy treatment.
For each patient undergoing radiation therapy, some form of image guidance is used during treatment. Depending on the area to be treated, normal organ motion may require daily image guidance, as is the case when treating the prostate, or more frequent imaging to guide radiation to fast moving organs, such as the lungs. Image guided radiation therapy enhances the ability to precisely target the tumor and protect nearby normal tissue by minimizing exposure to radiation.
Cleveland Clinic's Department of Radiation Oncology has been at the forefront of IGRT since the mid 1990s. Since then, we have acquired various imaging systems incorporating the newest technologies available to provide the most advanced patient care. Currently, we are equipped with image guided radiation therapy systems that use:
- Combined X-ray and optical imaging (Novalis, BrainLAB)
- Cone-beam computed tomography
- Electromagnetic emission detectors (Calypso system)
- Ultrasound imaging (RESTITU).
IGRT at Cleveland Clinic
M.D. News Special Feature by Robert Jansen
Radiation therapy for the treatment of cancer has come a long way over the past 20 years. The techniques for delivering external beam radiation to tumor sites have improved dramatically, mainly due to the use of ultrasound and/or localization computed tomography (CT) combined with special computer software to plan and guide individualized treatments. The result is that higher doses of radiation can be delivered more accurately to the tumor with the goals of better tumor control, higher survival rates, and fewer side effects.
John Suh, MD, is chairman of Cleveland Clinic's Department of Radiation Oncology, where ongoing clinical trial research studies help evaluate the impact of new treatment technologies on patient outcomes. Image-guided radiation therapy (IGRT) is one of those technologies, and Cleveland Clinic is a nationally recognized leader in the use of IGRT.
John Suh, M.D., is chairman of the Department of Radiation Oncology at Taussig Cancer Institute where ongoing clinical trials and research studies help determine the impact of new treatment technologies on patient outcomes
"IGRT employs and on-board imager in conjunction with a linear accelerator to provide a better method of delivering more accurate and precise radiation treatments," said Dr. Suh. "This becomes important in targets that move such as lung tumors and prostate cancer, and targets that are close to critical structures such as the spinal cord and brain."
Cleveland Clinic has been at the forefront of IGRT since the mid 1990s – first with the CyberKnife, which utilizes a light weight linear accelerator coupled to a robotic arm to target tumor for radiation therapy, and then with the BAT (B-mode acquisition and targeting) ultrasound, which allows a reproducible and robust method of accurately targeting the prostate and adjacent sensitive structures prior to radiation delivery.
In June 2004, Cleveland Clinic began evaluating another IGRT system (Novalis by BrainLAB) that incorporates two kV x-ray units recessed in the floor of the treatment vault and two ceiling-mounted amorphous silicon flat panel detectors. This unit is used mostly for cancers of the brain, spine, live, and lung.
A little over a year later, in November 2005, Cleveland Clinic was one of the first in the nation to use a three-dimensional (3D) ultrasound guidance system (Resonant Medical's RESTITU) with an image-guided platform for radiation treatment of the prostate. Similar to the BAT, this system quantifies changes in organ position and morphology from one treatment day to the next and enables more accurate patient positioning during treatment.
"One of the challenges radiation oncologists face is the delivery of radiation to a moving target, such as the lung and prostate gland," said Dr. Suh. "By using IGRT technology, we can more accurately and precisely deliver radiation."
The result if healthy and sensitive tissues, which do not need to be treated, can be spared much more effectively. Patients may also benefit from reduced side effects and improved clinical outcomes.
IGRT: Next Generation
Historically, tracking the position of the prostate gland and compensating for its movement during treatment was difficult. Not only is the prostate prone to change shape and shift its internal position, but it also moves as a result of normal processes, such as breathing and filling of the bladder and rectum.
The Calypso System sends an electromagnetic signal to activate the Beacon transponders implanted in the prostate. Signals return to the Calypso System, which calculates the position of the prostate continuously.
To address this issue, in August 2005 Cleveland Clinic began investigating a system (Calypso 4D Localization System) that utilizes internal fiducials or markers to more precisely localize the radiation dosage. Cleveland Clinic's involvement in the initial studies helped to lead to the approval of the device. When this system was FDA-approved in 2008, Cleveland Clinic was the first in Ohio to obtain it for clinical use for prostate cancer patients.
"The Calypso system functions as a GPS for the body, which is particularly useful for prostate cancer treatment," said Dr. Suh. "It involves implantation of Beacon transponders (tiny glass capsules, about the size of a grain of rice, containing electrical circuits) which, when activated by an electronic field, continuously track the position of the prostate prior to and during treatment in real time. They also show prostate motion."
Here's how the system works: Three tiny transponders are permanently implanted in the prostate. Signals from the transponders are analyzed by the localization system. The therapist is then guided by instructions on the system's touch-screen display to move the treatment target accurately to the position specified in the patient's treatment plan. The system remains in place during radiation delivery to track the position of the transponders and to identify motion.
"With the Calypso system, we have greater confidence that we're actually treating the intended target with tighter margins than we would use with other IGRT systems. This improved accuracy should result in fewer side effects and better outcomes for patients undergoing radiation therapy for prostate cancer," said Dr. Suh.
He explained that success rates with radiation are dependent on a number of factors including accuracy of treatment delivery, technologies utilized and experience and expertise of the medical staff. Cleveland Clinic has one of the largest prostate cancer databases of over 10,000 patients who have undergone surgery, brachytherapy, and radiation therapy. The department frequently reviews these treatment results to ensure the best outcomes possible.
Cleveland Clinic radiation oncologists utilized a combination of technologies to track the location of the prostate before and during treatment. These include cone beam CT to help identify the bladder and rectum prior to treatment, the Calypso system to detect the real time motion of the prostate, and the Clarity (by Resonant Medical), which uses ultrasound to obtain a snapshot of the prostate's location prior to treatment.
Cleveland Clinic radiation oncologists utilize a variety of technologies to track the location of tumors before and during treatment. Shown here is Rahul Tendulkar, M.D. with the Clarity System, available in Ohio only at the Taussig Cancer Institute.
The Clarity is FDA - approved for image guidance in the planning and treatment of prostate cancer and breast cancer, and Cleveland Clinic uses it for both. According to Dr. Suh, it may be useful for identification of the lumpectomy cavity which allows for more accurate delivery of partial breast irradiation (PBI).
Radiation therapy is an important treatment option for women with breast cancer. For those with early stage disease, removal of the tumor followed by radiation therapy is equivalent to removal of the breast with mastectomy in terms of outcomes," he said. "Recently, there has been growing interest in performing PBI to treat the lumpectomy or surgical cavity in some patients. This involves radiation therapy two times a day, separated by six hours, for five days as opposed to the traditional radiation treatment schedule of one treatment per day, Monday through Friday, for five to six and a half weeks."
The Clarity breast system, according to Dr. Suh, allows radiation oncologists to account for changes in the size, shape and position of the target (the lumpectomy cavity) based on visualization of the actual anatomy. Ultimately, this helps to ensure proper delivery of radiation to the target. Another advantage for the patient is its noninvasiveness – there is no need to place fiducials in the breast. And, unlike CT, it does not use ionizing radiation.
"We obtained the Clarity, the Calypso, and other image guidance systems using specialized radiation machines to improve our outcomes in terms of tumor control, to minimize side effects and to improve the patient experience by decreasing treatment times and allowing for a shorter course of radiation treatment."
For the past three years, shorter course radiation treatments using IGRT have also been available at Cleveland Clinic to select patients with spinal metastases. Rather than undergoing invasive surgery followed by 10 to 15 sessions of daily radiation treatments over a period of several weeks, patients receive a single high-dose of precisely delivered radiation. Millimeter accuracy is required and the ExacTrac IGRT system by BrainLAB delivers this by using micro-multileaf collimators and image guidance.
The Elekta Synergy S is another system utilized by Cleveland Clinic for small-field targets, such as brain tumors, prostate cancer and other tumors requiring tight treatment margins. The Synergy S employs an image-guided robotic linear accelerator for advanced stereotactic radiation treatments via highly conformal beam shaping. This machine complements the highly successful Gamma Knife radiosurgery program for intracranial disease such as brain metastases, benign brain tumors, trigeminal neuralgia, and arteriovenous malformations.
Siemens' Artiste Solution is yet another linear accelerator in Cleveland Clinic's IGRT arsenal. Engineered specifically for Adaptive Radiation Therapy, this system offers multiple imaging modalities, including megavoltage (MV) images and eventually kilovoltage (kV) radiographs, allowing physicians to choose the imaging modality that best complements each case.
"In terms of technology, Cleveland Clinic is fortunate to be able to choose from a wide array of vendors to individualize and optimize patient care. This flexibility is especially valuable when treating difficult cases that are seen in major referral centers like ours," Dr. Suh explained. "We're continually evaluating the various technologies to provide better care for our patients."
Continually Improving Results
To further improve the results of IGRT, Cleveland Clinic radiation oncologists are utilizing hyperthermia. By heating the surface of the tumor to temperatures of approximately 42.5 degrees Celsius, blood flow to the tumor is increased. This, in turn, increases oxygen flow, which increases sensitivity to radiation treatment.
Hyperthermia has been employed at Cleveland Clinic since mid-2008 for select gynecologic malignancies, recurrent chest wall malignancies related to breast cancer, sarcomas, and some head and neck cancers. Clinical results of these initial experiences with hyperthermia have been very encouraging, according to Dr. Suh.
"Our patients have benefited from the wide range of technologies that we have at our disposal," he said. "These cutting edge technologies, coupled with our multidisciplinary approach to cancer care and commitment to research and education, provide better patient outcomes and experiences. Ultimately, the people behind the technologies remain important to our continued success against cancer."