European Nuclear Medicine Guide
Although being applied since the second half of the 20th century, iNM has seen substantial growth over the recent years, and not only in the implementation of well-known strategies. To date, the use of iNM has been successfully expanded into a variety of mostly oncological clinical indications. The most distinct iNM methods that are based on local accumulation of an administered radiopharmaceutical are:
Sentinel lymph node surgery - identification of micro-metastatic (< 2mm) nodal spread in clinically node negative patients: Local administration of a radiopharmaceutical nanoparticle (generally, 99mTc gamma -emitters) at the site of a primary cancer or scar thereof is followed by lymphatic migration of the administered radiopharmaceuticals. This migration that is driven by the natural flow of lymphatic fluid results in transportation to the first tumor draining lymph nodes, also called sentinel lymph nodes (SLN). In these nodes accumulation of tracer molecules is facilitated via i.e., phagocytosis by residing macrophages. Combined preoperative (lymphoscintigraphy and SPECT) imaging and RGS enables accurate patient staging by allowing minimally invasive lymph node biopsy of the nodes that are most likely to harbor metastasis [7-11].
Targeted tracer surgery - identification of macro-metastatic (> 2mm) nodal spread in clinically node positive patients: Preoperative receptor-targeted PET imaging provides the means to identify nodal macro-metastasis and surgical planning based on their location. Intraoperative identification of these lesions requires systemic administration of a radiopharmaceutical analogue of the original PET tracer prior to the surgical intervention. Alignment of the receptor affinity and pharmacokinetics of the radiopharmaceutical (generally, 99mTc gamma-emitters) with what was seen during diagnostic PET ensures active intraoperative guidance toward tumor lymph nodes using RGS [12-14].
Targeted tracer surgery - identification of primary tumor margins and local recurrences: The methodology used to identify macro-metastases also helps provide a successful strategy for identification of primary tumor margins and local recurrences, either in vivo or during ex vivo back-table scanning. In the latter, the imaging information of the specimens is relayed back to the operating surgeon, rather than the surgeon performing the imaging in real-time during the intervention [15, 16].
Image guided biopsy: Both SLN- and receptor-targeted tracers can be used to guide the execution and validate the accuracy of needle biopsies. Herein both beta- and gamma-emitting pharmaceuticals can be used, depending on the diagnostic NM modality selected to identify the lesions of interest [17-19].
Local marking of lesions: Radiologically defined lesions can be marked under CT or US guidance, using a 99mTc-radiopharmaceutical with micro- or nanoparticles, or using iodine(125I)-containing titanium seeds. These methodologies are often unified under the names of Radioguided Occult Lesion Localization (ROLL) and Radioguided Seed Localization (RSL) [20, 21].
This strategy is mainly be used to guide resection of the lesion itself, but that can also be used to support the demarcation of lesions in a neoadjuvant setting [22,23].
Liver radioembolization: While markedly different in application, iNM is a critical component during theranostic liver radioembolization.
Firstly, CT-guided intra-arterial administration of radiopharmaceutical microparticles in the hepatic artery allows for shunting to be identified using imaging and dosimetry to be performed. Thereafter, dosimetry allows personalization of the delivery of therapeutic radiopharmaceutical (e.g., 90Y or 166Ho) microspheres [24-25].