IGRT: Imaging Targets Better Therapy

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Image guided radiation therapy (IGRT) is bringing with it a lot of buzz to the field of radiation therapy. IGRT captures real-time images minutes before treatment is delivered to the patient. Clinicians compare the images to treatment plans and make any necessary positioning adjustments so that the tumor is directly in the path of the beam. With IGRT, radiation oncology teams are better hitting the target, all the while gaining the confidence they need to increase doses, permeate the tumor and significantly decrease the side effects of radiation treatment.

As more and more cancer treatment centers throughout the United States add newer hardware and software capabilities to their arsenal of radiotherapy devices, treatment options for patients are expanding and rates of complications due to the side effects of radiotherapy are falling. Advancements in both the planning and the delivery stages of radiation oncology are giving radiotherapy teams the clinical confidence they need to go after the toughest of tumors; including masses intertwined with critical structures and tumors that have unsuccessfully undergone some other form of treatment.

Perhaps one of the most talked-about radiation oncology technologies on the market today is image guided radiation therapy (IGRT). IGRT allows images - created via ultrasound, x-ray, fluoroscopic or cone beam computed tomography - to be acquired immediately before a patient receives treatment to confirm that the beam is going to hit the intended target. Regardless if the patient is repositioned one, three or even seven millimeters back on target, IGRT enables radiation treatment to be delivered more accurately and at higher doses to eradicate the tumor.

Ultrasound-guided IGRT   

In radiotherapy, doctors use ionizing radiation to kill cancer cells and shrink tumors. Intensity modulated radiation therapy (IMRT) takes external beam radiation therapy a step further than its predecessor, 3D conformal radiation therapy (3D-CRT). IMRT employs computer-generated images in an increased level of accuracy by matching radiation to the size and shape of a patient's tumor.

It's an iterative, time consuming process, but IMRT has the amazing ability to be exceedingly precise within millimeters, according to Michael Steinberg, MD, medical director at Santa Monica Cancer Treatment Center (SMCTC) in Santa Monica, Calif. "With conventional radiotherapy, we were precise within about 20 millimeters, meaning we had to put margins of two centimeters around the target just to make sure we were hitting it everyday," he says. "When 3D-CRT came along, precision got down to seven and 10 millimeters. IMRT is literally precise between one and three millimeters."

While IMRT has the potential to deliver high doses of radiation that permeate to the tumor while also missing critical structures, the addition of IGRT allows clinicians to carefully evaluate tumor motion throughout a patient's elongated treatment process. A significant problem in radiotherapy, tumor motion is attributed mostly to involuntary changes in patient anatomy that occur over the course of daily treatments and variation in patient set up.

To compensate for target movement in prostate cancer patients, clinicians at SMCTC are using NOMOS Radiation Oncology's BATCAM, an ultrasound image guidance tool, in conjunction with IMRT. The BAT combines ultrasound and a 3D tracking system with a touchscreen-based treatment room interface to non-invasively pinpoint tumor targets at the time of a radiation therapy treatment.

After patients are immobilized on the couch, Steinberg says that ultrasound images acquired via BATCAM are compared with fused MR/CT data sets that are acquired during treatment planning. "If the patient needs to be adjusted, the computer will actually [determine] how far off the patient is from the reference point from the original set up," says Steinberg. "The system will tell you to move the patient 4 millimeters in x direction, 5 millimeters in the y direction and 6 millimeters in the z direction.

"IMRT offers unprecedented precision and we add IGRT with the BATCAM, which localizes the prostate accurately each day of treatment to make sure that the highly precise dose gets to where it is intended," continues Steinberg. "With regards to dose escalation, it turns out that higher dose eradicates and cures more prostate cancer. The problem is that there are sensitive normal structures around the prostate like the bladder and rectum. By adding