Feasibility Animal Study of Novel ICG Sentinel Node Detection Technique in Head and Neck Region

Objectives: Sentinel node biopsy (SNB) allows head and neck surgeons to avoid unnecessary neck dissection. The popular SNB method using radioisotope (RI) has some drawbacks, such as the strict legal regulations for RI use in Japan. Recently, the SNB technique using real time indocyanine green (ICG) fluorescence image has become prevalent in breast cancer testing. Some reports demonstrated improved detection sensitivity with this method. However, the major problem of ICG method is its quick migration through the lymphatic system, which results in a limited diagnostic time window and detection of downstream subsequent nodes. To overcome this problem, we modified the ICG detection method by making ICG-colloid and demonstrated the feasibility of this technique in a mouse model. Methods: ICG-colloid was formed by mixing ICG and phytate colloids, which are commercially available as a kit for 99mTc-radiocolloid. Twenty microliters of ICG or ICG-colloid was injected into the tongue of a nude mouse, and the fluorescent images were observed with time until 48Hrs after injection. The fluorescence intensity in detected SN was analyzed. Results: In ICG injected animals, SNs were detected soon after injection, and second echelon lymph nodes were detected after 30-60min. In ICG-colloid injected animals, SNs were also detected after 30-60 min, and no second echelon lymph node was detected. Peak fluorescence intensity was 6-12Hr in both animal groups. No SN was detected after 24Hr in ICG animals, whereas SNs were still detectable in ICG-colloid animals. Conclusions: SNB using ICG-colloid technique may have advantages of prolonged diagnostic time window and prevention of downstream subsequent node detection.