In vivo detection of tumor-infiltrated axillary lymph nodes with a handheld beta-sensitive probe: A phantom study

Sentinel node biopsy utilizing Technetium-99m-labeled sulfur colloid is rapidly becoming a standard part of the surgical treatment of breast cancer. Although this method is effective in identifying sentinel lymph node(s) in the axilla, the non-tumor-specific nature of colloids necessitates removal of the node(s) for subsequent analysis. Tumor-specific radiotracers, such as positron-emitting Fluorine-18-labeled Fluorodeoxyglucose (FDG), have been used with positron emission tomography (PET) to successfully stage breast cancer. Thus, the use of FDG with a handheld probe optimized for detection of beta particles could perhaps help identify cancer-infiltrated nodes during axillary dissection. In this study the ability of a new solid-state beta-sensitive probe to identify tumor-infiltrated lymph nodes was investigated in a phantom study. The axilla and tumor-infiltrated lymph nodes were simulated with gelatin phantoms containing FDG concentrations commonly reported from PET studies. FDG uptake in the organs of a patient was simulated with an anthropomorphic torso phantom. Following examination by the handheld probe, a PET image of the phantom was acquired. The results demonstrated that the probe was capable of identifying lymph nodes containing as little as 10μl of tumor. This amount of simulated tumor was too small to be detected by the PET scanner. This method, therefore, may be useful in intraoperatively identifying some tumor-infiltrated axillary lymph nodes not detected with PET; potentially increasing the efficiency of axillary dissection. Future clinical trials must be performed to assess the utility of this new technique.