SPECT/CT helps identify breast cancer in overweight women
The survival rate for breast cancer is very good if it is detected before it has spread to other parts of the body. Newly diagnosed patients often have a negative axillary sentinel node biopsy — a minimally invasive surgical procedure — to see whether the cancer has spread to lymph glands under the arm. However, the procedure sometimes fails to identify the sentinel node — the one that traps cancer cells that drain away from the breast lesion site.
Most often this failure is in overweight and obese patients, and it can lead to unnecessary surgeries and inaccurate therapies. Dr. Hedva Lerman and her colleagues from Tel-Aviv Sourasky Medical Center in Israel investigated whether combining single-photon-emission CT (SPECT)/CT with lymphoscintigraphy would improve sentinel node identification in overweight breast cancer patients.
Researchers found that using SPECT/CT imaging helps identify lymph nodes that trap cancer cells in overweight or obese women. Planar images did not identify a hot lymph node (A). CT, SPECT and fused images are shown from left to right, and a node was clearly identified (arrow) in the fused image (B). Reprinted with permission from the Society of Nuclear Medicine Inc.
Lymphoscintigraphy is becoming a more common method for identifying the sentinel lymph node. It involves the injection of the blue dye Tc-rhenium colloid, which makes the lymphatic vessels and sentinel node visible on a computer screen prior to surgery and traceable with a handheld gamma camera during the operation. But in many overweight patients, the nodes are not detectable. These women may then receive an unnecessary axillary lymph node dissection — a complex surgery that involves removing all of the lymph nodes in the armpit region — even though obesity puts them at higher risk for postsurgical complications.
Because SPECT provides quality imaging and CT provides information on anatomic landmarks, the researchers wanted to see if combining the two techniques with lymphoscintigraphy could identify the node hot spots better than lymphoscintigraphy by itself. They tested 220 women who had invasive breast cancer with both planar lymphoscintigraphy imaging and the combined SPECT/CT lymphoscintigraphy technique.
They injected a dose of Tc-rhenium colloid into the tumor sites of each patient. They took lymphoscintigraphy planar images and SPECT/CT lymphoscintigraphy combined images immediately after injection and continued imaging for up to 24 hours until the hot sentinel nodes were identified. For 160 of the patients, they used a Hawkeye SPECT/CT system, and for the other 60 patients they used an Infinia/Hawkeye hybrid system, both from GE Healthcare.
The planar lymphoscintigraphy images identified the nodes in 171 patients who had a body mass index of about 25.2 (slightly overweight), but failed to do so in 49 patients with a body mass index of about 28 (very overweight). However, in 29 of the latter patients, the SPECT/CT method identified the hot sentinel nodes. Overall, SPECT/CT identified the hot sentinel nodes in 91 percent of all the patients, including the 29 whose nodes were not detected with planar lymphoscintigraphy.
The researchers believe their results indicate that adding SPECT/CT to lymphoscintigraphy helps improve the identification of sentinel nodes, especially for overweight or obese patients. They believe that improved identification will reduce false-positive interpretations and unnecessary surgeries.
The Journal of Nuclear Medicine, February 2007, pp. 201-206.
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