Toward optimization of imaging system and lymphatic tracer for near-infrared fluorescent sentinel lymph node mapping in breast cancer

Abstract

Background: Near-infrared (NIR) fluorescent sentinel lymph node (SLN) mapping in breast cancer requires optimized imaging systems and lymphatic tracers.

Materials and methods: A small, portable version of the FLARE imaging system, termed Mini-FLARE, was developed for capturing color video and two semi-independent channels of NIR fluorescence (700 and 800 nm) in real time. Initial optimization of lymphatic tracer dose was performed using 35-kg Yorkshire pigs and a 6-patient pilot clinical trial. More refined optimization was performed in 24 consecutive breast cancer patients. All patients received the standard of care using (99m)Technetium-nanocolloid and patent blue. In addition, 1.6 ml of indocyanine green adsorbed to human serum albumin (ICG:HSA) was injected directly after patent blue at the same location. Patients were allocated to 1 of 8 escalating ICG:HSA concentration groups from 50 to 1000 μM.

Results: The Mini-FLARE system was positioned easily in the operating room and could be used up to 13 in. from the patient. Mini-FLARE enabled visualization of lymphatic channels and SLNs in all patients. A total of 35 SLNs (mean = 1.45, range 1-3) were detected: 35 radioactive (100%), 30 blue (86%), and 35 NIR fluorescent (100%). Contrast agent quenching at the injection site and dilution within lymphatic channels were major contributors to signal strength of the SLN. Optimal injection dose of ICG:HSA ranged between 400 and 800 μM. No adverse reactions were observed.

Conclusions: We describe the clinical translation of a new NIR fluorescence imaging system and define the optimal ICG:HSA dose range for SLN mapping in breast cancer.

Trial registration: ClinicalTrials.gov NCT00721370.

Fig. 1

The Mini-FLARE portable near-infrared fluorescence imaging system. a Imaging system, composed of electronics/monitor cart and counterweighted imaging system pole. b Sterile drape/shield attached to the imaging head with other major parts identified. c Excitation and emission light paths, and filtration for the Mini-FLARE imaging system. DM, 650 nm dichroic mirror

Fig. 2

Optimization of ICG:HSA dose as a function of the complex trade-off between fluorescence quenching at the injection site and dilution of fluorophore in lymphatic channels. a Preclinical studies in Yorkshire pigs. Subcutaneous injection sites (left; white arrows) showing quenching and resected SLNs (right) showing NIR fluorophore dilution for increasing concentrations of ICG:HSA. For each are displayed color video (left columns) and 800 nm NIR fluorescence (right columns) images obtained using 760 nm excitation light at 7.7 mW/cm². All camera exposure times were 45 ms. Data are representative of n = 3 pigs. b Optimization of ICG:HSA dose for breast cancer SLN mapping: Signal-to-background ratio (mean ± SD) of the SLNs (ordinate) as a function of injected dose of ICG:HSA (abscissa) in women undergoing SLN mapping for breast cancer. Statistical comparisons are: 200 vs. 400 μM, P = .001; 200 vs. 500 μM, P = .001; 200 vs. 600 μM, P < .0001; 200 vs. 800 μM, P = .001; 1000 vs. 400 μM, P < .0001; 1000 vs. 500 μM, P < .0001; 1000 vs. 600 μM, P < .0001; 1000 vs. 800 μM, P < .0001. The SBRs of the 400, 500, 600, and 800 μM concentration groups were not significantly different, although a trend was found favoring the 600 μM concentration group (500 vs. 600, P = .06)

Fig. 3

Real-time NIR fluorescence imaging during sentinel lymph node mapping in women with breast cancer: Shown are typical in vivo (top row) and ex vivo (bottom row; postresection) results from a subject injected with 500 μM ICG:HSA. White arrow identifies the SLN. NIR fluorescence (left) and pseudocolored (lime green) merge with the color video image (right). Exposure times were 50 ms for in vivo images and 30 ms for ex vivo images. 760 nm excitation fluence rate was ~7.7 mW/cm² for all images. Scale bars indicate 1 cm