High Noon For Breast Tumors
Picture this scene: Our Hero and The Villain agree to a shoot-out at dawn. They are matched in their deadly skill with pistols and know that one of them will die. At sunrise they step into the street as citizens peer out their windows. They have agreed to draw their guns when the clock strikes the hour - but just as it does, someone throws a blanket over the head of each gunslinger. Unable to see their targets, they fire into the air before them, not knowing where the bullets will fly.
During radiation therapy, your tumor site - the villain - will be targeted with ionizing energy by your radiation therapist - the hero. Just like flying bullets, radiation beams will impact both healthy and cancerous tissue. So when you are fighting cancer with radiation, it is important to see your enemy and hit the target accurately. But a tumor is hidden within your tissues, so some kind of imaging technology must be used to find the target.
Imaging the Elusive Target
Your radiation oncology team will carefully plan your treatment, based on your diagnosis and the size, shape, and location of your target area. There are several ways to get a glimpse of your radiation target area - you may have a CT (computed tomography) scan, an MRI (magnetic resonance imaging), or a PET (positron emission tomography) scan. Those imaging techniques are usually taken before treatment begins. Port films - special X-ray images - may be taken at regular intervals to assess the treatment site. But tumors and tissue can shift and shrink between treatments, so scientists have come up with a way to use images to keep track of these changes and guide the radiation just where it is needed.
Image Guided Radiation Therapy: Look While You're Shooting
Image-guided radiotherapy (IGRT) is a technique that gives your radiation therapist a view of your tumor site just before or even during treatment sessions. This computer-generated picture may combine several types of imaging techniques to produce a current and complete virtual model of the treatment site. This image is used to guide and shape the radiation beam for your treatments. If your tumor site changes, the radiation beam can be modified to match it, sparing healthy tissue from exposure to radiation. IGRT improves the accuracy of treatments such as 3D Conformal breast radiation and intensity modulated radiotherapy (IMRT), two types of external beam radiation.
The Clarity System of image guidance for radiotherapy blends 3D ultrasound images with pretreatment CT images for radiation planning. "Clarity provides the first method of daily lumpectomy monitoring that is based on visualization of the actual anatomy-rather than an estimation of the location of the cavity," said Dr. Tony Falco of Resonant Medical. "This additional precision may enable physicians to tighten radiation margins around the breast or lumpectomy cavity, thereby minimizing radiation exposure to healthy tissue and organs such as the lung and the heart."
Pros and Cons of IGRT
Image guidance for radiation therapy is used for prostate, pancreatic, head, neck, lung, and breast cancers. IGRT fine-tunes the precision with which the radiation is aimed at your treatment site and margins - the area in which recurrence is most likely. As the target changes, the radiation can be adapted to hit the treatment site and spare healthy tissue. You have fewer side effects and faster recovery as a result of more accurately aimed therapy. Dr. Laura Dawson writes, " One of the largest dosimetric advantages of image-guided radiotherapy is the reduction in variability of dose delivered to the tumor and healthy tissues at the time of treatment - so the prescribed dose is much more likely to be delivered as planned."
IGRT takes more time and labor than standard breast radiation during setup for each treatment. Despite its name, image guidance for radiation therapy is not actually a treatment, but is part of treatment planning. IGRT will cost more than radiation guided by tattoos or port films, and your appointments will take more time. You might not be offered radiation with IGRT if your clinic does not have the equipment, trained staff, technology support, and data storage capability necessary to support the use of image-guided radiotherapy. As promising as IGRT sounds, it is not a perfect technology and can't guarantee ideal results, but it has exciting possibilities and researchers expect it to improve over time.
Take-Home Points About Image Guided Radiation Therapy
Image guidance for radiation therapy increases accuracy of breast radiation planning and treatment, as well as sparing healthy tissue. If you're having 3D Conformal or Intensity Modulated Radiotherapy for breast cancer, IGRT will be used as guidance for the radiation beam. Like radiation, image guidance is painless to you, but improves the aim of cancer-killing energy to your tumor.
IGRT Definition. Dictionary of Cancer Terms. National Cancer Institute.
Image-guided radiotherapy: rationale, benefits, and limitations. Dr Laura A Dawson MD, Michael B Sharpe PhD. The Lancet Oncology, Volume 7, Issue 10, Pages 848 - 858, October 2006.
Overview Of Image-Guided Radiation Therapy. Lei Xing, Ph.D., Brian Thorndyke, Ph.D., Eduard Schreibmann, Ph.D., et al. Medical Dosimetry, Vol. 31, No. 2, pp. 91-112, 2006.
Personal correspondence with Tony Falco, PhD, FCCPM, Chief Executive Officer Resonant Medical. April 27, 2010.