Detection of sentinel node in breast cancer: Pilot study with the imaging probe

The commonly used gamma probes are easy to use but also give rough informat ion when employed in radioisotope-guided surgery. When images are required for exact localization, a gamma camera as well as a probe have to be used. Position-sensitive photomultipliers have contemporaneously allowed high-res olution scintigraphy and miniaturization of gamma cameras. We have assemble d a miniature gamma camera with a 1-square-inch field of view and an intrin sic resolution of about 1 mm. When the minicamera is collimated with a larg e-holed, highly sensitive collimator, it acquires a spatial resolution of 3 mm. This prototype has been tested in the detection of difficult-to-image breast cancer sentinel nodes. Five nodes that had not been found with the u sual technique of an Anger camera plus conventional probe were checked with the miniature camera that we named imaging probe: it actually is small eno ugh to be used as a probe and large enough to give an image. One of the fiv e nodes was found and imaged. It was small, disease-free, close to the tumo r and probably hidden by the Compton halo around the peritumoral injection site. Our pilot study shows that the imaging probe, although still a protot ype, has certain advantages over conventional methods when lymph node local ization is required during surgery.