Cancer Treatment Technology at Rutland Regional
Image Guided Radiation Therapy is a new technique which utilizes radiographic imaging to increase the precision of radiation therapy.
Prior to this innovation, radiation therapy has been localized using x-ray pictures (or radiographs) of the bones within the body and external tattoos. The issue with radiographs is that the tumor often cannot be seen on the radiograph. In many cases the tumor is composed of tissue which is less dense than bone, and equal in density to the surrounding normal tissues. Radiographs give a picture based on density within structures so the tumor is often not seen. Bony landmarks are used as a surrogate for the tumor for localization of the tumor. As you can imagine, if there is any movement in the tumor’s position, the radiation could indeed miss a portion of the intended target.
Image Guided Radiation Therapy (IGRT) uses special radiographic techniques to localize the tumor on a daily basis. By knowing where the tumor is, we can potentially increase our precision. This gives the potential for higher doses of radiation to the tumor, while treating less normal surrounding tissue and thereby reducing side effects and complications. There are various types of IGRT, those employing ultrasound, radiographs or CT scanners.
At Rutland Regional Medical Center, we have employed ultrasound techniques in our IGRT service. Our unit is made by North American Scientific (Nomos) and is named the BAT system. This unusual name is an acronym for B mode Acquisition and Targeting, a phrase which, in technical jargon, describes how the unit works.
In lay terms, the concept is better understood. The prostate is an excellent organ to discuss. If a man with prostate cancer has radiation therapy, that therapy is designed with CT scans and computers to treat the prostate region as precisely as possible. A technique called Intensity Modulated Radiotherapy designs the treatment using beams from many directions to sculpt the radiation treatment to the desired region. The issue with all this precision is that the only point in time when we know the prostate position is at the moment of the CT scan. Minutes later the bladder has more urine in it, pressing on the prostate from the top. Hours later there is a bowel movement in the rectum, pressing the prostate forward. Thus, the prostate can move within the body slightly and this movement must be accounted for. With conventional radiation this movement is compensated for by treating a larger area. This potentially can increase the risk of side effects, or complications.
Ultrasound is a non-invasive imaging system to look deep into the body. As any woman who has had an ultrasound during pregnancy knows, the technique is simple, painless and requires no further radiation. Ultrasound cannot examine every part of the body and air cavities and bone structures can interfere with the picture, but the abdomen is an area where ultrasound is especially useful. Each day when the man receives his radiation treatment, the BAT unit is used. An ultrasound is done three dimensionally of the prostate. The ultrasound machine probe has several infrared light targets on it so that it can be located in space. In the treatment room there is a stereoscopic infrared camera which can locate the ultrasound, and thus the prostate, and adjust the patient’s prostate position to the original position on the day of the CT scan. Urine volume, stool volume and prostate position are thus eliminated from variability for the treatment. This gives the radiation therapy treatment a new, previously unattainable precision. This precision can allow less treatment to normal surrounding structures. It is these surrounding structures which give radiation therapy its side effects and potential for complication. By reducing the risk, we can increase the dose of this cancer-fighting treatment. The BAT unit consists of the ultrasound machine, stereoscopic camera and targeting system. It can be used for any tumor site which can be imaged with ultrasound.
Image Guided Radiotherapy is an ideal treatment option for some tumor sites. Only an oncology team can determine the proper mix of surgical oncology, medical oncology, and radiation oncology treatments. If radiation therapy is an option for a patient, treatment planning will determine whether IGRT is ideal for that patient. It is just one of the specialized techniques of modern radiotherapy delivery.
Rutland Regional Medical Center, which previously brought Intensity Modulated Radiotherapy to Vermont, was the first hospital within Vermont to offer Image Guided Radiotherapy.
To learn more, contact the Community Cancer Center at Rutland Regional at 802.747.1831.
By
Richard D. Lovett, MD, Radiation Oncologist
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