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EXECUTIVE SUMMARY Nuclear medicine is an essential tool in the delivery of high-quality medical care, going beyond simple anatomical imaging to the use of physiological processes for both imaging and therapy. Nuclear medicine techniques were applied to the lymphatic system as early as the 1950s by Sherman et al. (1), using 198Au colloid (a beta emitter) as a therapeutic agent for lymph node metastasis. In the late 1960s and early 1970s, the ready availability of technetium-99m (99mTc) allowed more widespread lymphatic imaging (lymphoscintigraphy) with 99mTc colloid. In 1976, Ege (2) studied lymphatic flow in 848 patients, suggesting lymphoscintigraphy could demonstrate variable lymphatic drainage patterns, therefore allowing more accurate radiation therapy fields. In recent years, advances in radiopharmaceuticals and imaging technology have allowed more accurate localization of lymph nodes during lymphoscintigraphy and the development of the sentinel lymph node (SLN) concept. One of the first mentions of SLN was made in 1960 by Gould and Philben (3). They described a specific location of a node that drained the parotid gland. This node, located at the junction of the anterior and posterior facial veins, was described as the node most likely to contain metastasis. It was recommended that this node be investigated first before carrying out complete node dissection (3). The SLN concept was further explored by Cabanas (4) in 1977 when lymphangiography with contrast was used to identify a specific location for lymphatic drainage from the penis. Similar to what was described by Gould and Philben, Cabanas (4) felt that this 1 specific lymph node (located at the superficial epigastric vein by Cabanas for penile carcinoma) could be defined as the SLN for all patients. Individual variations demonstrated in the lymphatic channels and the location of the sentinel node since the initial investigations have confirmed that mapping of lymphatic drainage needs to be carried out for each patient undergoing SLN sampling. SLN identification can be done with optical agents, such as isosulfan or methylene blue, as well as with radiotracers and fluorescent tracers. Localization of the SLN(s) with these techniques in individual patients has allowed a more focused investigation of nodal drainage from a primary tumor site, preventing the morbidity and mortality of complete node bed dissection in patients with no clinical evidence of tumor in the regional nodal basin (5). One difficulty with reviewing the literature describing lymphoscintigraphy is the variety of tracers in use around the world and throughout the history of lymphoscintigraphy. Smaller particles tend to move through the lymphatics more quickly. Some tracers are more likely to stop at the first node they encounter, while others are more likely to move through the lymphatic system more readily, demonstrating channels, node beds, and central lymphatic structures. The tracer used depends on the clinical indication (e.g., sentinel node scintigraphy, lymphedema, or lymphatic vessel integrity), as well as availability and local regulations. In the United States, there are only 2 tracers generally available for clinical use: 99mTc sulfur colloid and 99mTc tilmanocept. In addition, injection techniques, imaging protocols, and camera technology can vary substantially, making comparisons between studies challenging. A discussion of these technical differences is beyond the scope of this document. These appropriate use criteria (AUC) have been developed to describe the appropriate use of radiopharmaceuticals for lymphoscintigraphy in SLN mapping and lymphedema. It is hoped that through these recommendations, nuclear medicine lymphatic imaging techniques will be used to benefit patients in the most cost-effective manner. Representatives from the Society of Nuclear Medicine and Molecular Imaging (SNMMI), the Society for Vascular Medicine (SVM), the Australia and New Zealand Society of Nuclear Medicine (ANZSNM), the American College of Radiology (ACR), the Society of Surgical Oncology (SSO), the European Association of Nuclear Medicine (EANM), the American Head and Neck Society (AHNS), the American Society of Clinical Oncology (ASCO), the American Society of Breast Surgeons (ASBrS), the American College of Nuclear Medicine (ACNM), and the American College of Surgeons (ACS) assembled as an autonomous workgroup to develop these AUC. This process was performed in accordance with the Protecting Access to Medicare Act of 2014 (6). This legislation requires that all referring physicians consult AUC by using a clinical decision support mechanism before ordering any advanced diagnostic imaging services. Such services are defined as diagnostic magnetic resonance imaging (MRI), computed tomography (CT), and nuclear medicine procedures, including positron emission tomography (PET) and others, as specified by the Secretary of Health and Human Services in consultation with physician specialty organizations and other stakeholders (3). Lymphoscintigraphy usually causes trivial radiation exposures for the patient, the surgeon, and the staff handling any specimens that may contain radioactivity. Local regulations that address the handling of radiopharmaceuticals and exposure of the public should always be followed. Radiation exposures are also trivial for pregnant patients and infants exposed to someone who has been injected with lymphoscintigraphic agents labeled with 99mTc. The amount of radiopharmaceutical transferred from the interstitium into the blood and from the blood to the milk is very low. However, when performing an SLN procedure for breast cancer, it seems prudent to recommend the interruption of direct breastfeeding for 24 hours after administration of the radiopharmaceutical. There is a potential for more fetal or infant exposure if the radioisotope dissociates from the radiopharmaceutical; however, exposures will remain very small and likely of no consequence. The rapid decay of 99mTc (6-hour half-life) also allows for rapid return of radiation exposures to background levels within a short time. More detailed information can be found in the document “Advisory Committee on Medical Uses of Isotopes (ACMUI) Sub-Committee on Nursing Mother Guidelines for the Medical Administration of Radioactive Materials” (https://www.nrc.gov/docs/ML1803/ML18033B034.pdf).