Background: Near-infrared (NIR) fluorescence-guided sentinel lymph node biopsy (SLNB) using indocyanine green (ICG) has been successfully applied in various kinds of cancers, especially in breast cancer. Optimizing the concentration of ICG without using human serum albumin in natural lymphatic system is still required.

Methods: 25mg of ICG was diluted with distilled water (DW) or normal saline (NS). Dilution concentrations used for measurement were 0.25μg/mL, 0.5μg/mL, 2.5μg/mL, 5.0μg/mL, 25μg/mL, and 250μg/mL. The brightness of fluorescence was measured by an image system called Visual Navigator (SH System, Korea). We used graphic software (GIMP, version 2.8.14, The GIMP Team) to measure the brightness. We assumed that drained serous lymphatics from a breast cancer patient can reflect a natural lymphatic condition injected with ICG in the operation field. Drained lymphatics were mixed to reduce the concentration of ICG by half that was diluted with DW or NS. We also measured the brightness of fluorescence diluted with DW or NS that was mixed with drained lymphatics. After this screening test, we subdivided the range which brightness was measured as 100 and adjusted the intensity of illumination for more specific results.

Results: Highest brightness values were measured as 100 between 2.5μg/mL and 25μg/mL concentration of ICG with DW dilution in screening settings, and the values of brightness were measured as 100 between 2.5μg/mL and 5.0μg/mL concentration of ICG with NS dilution. When drained lymphatics were mixed together, the values of brightness were measured as 100 between 2.5μg/mL and 25μg/mL concentration of ICG with DW or NS dilution. After subdividing the ICG concentration to 2.5μg/mL, 3.13μg/mL, 5.0μg/mL, 6.25μg/mL, 12.5μg/mL and 25μg/mL with adjusting the intensity of illumination, the highest brightness value was measured as 76 in 5.0μg/mL concentration of ICG with DW dilution. When diluting with NS, the highest brightness value was measured as 61 in 5.0μg/mL ICG concentration. After mixing with drained lymphatics, the highest brightness value was both 79 in 5.0μg/mL concentration of ICG with DW and NS dilution.

Conclusions: This study showed a practically optimal ICG concentration range in fluorescence guided SLNB. The optimal range of ICG concentration is from 3.13μg/mL to 6.25μg/mL with DW or NS dilution. Although 5.0μg/mL met the best result, adjustment for individual settings may be considered.

Citation Format: Paik H-J, Yi HW, Park S, Ryu JM, Nam SJ, Lee JE, Kil WH, Lee SK, Bae SY, Kim SW. Optimal concentration of indocyanine green in near-infrared fluorescence guided sentinel lymph node biopsy in breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-01-03.