Optimization of Second Window Indocyanine Green for Intraoperative Near-Infrared Imaging of Thoracic Malignancy

Abstract

Background: Near-infrared (NIR) imaging using the second time window of indocyanine green (ICG) allows localization of pulmonary, pleural, and mediastinal malignancies during surgery. Based on empirical evidence, we hypothesized that different histologic tumor types fluoresce optimally at different ICG doses.

Study design: Patients with thoracic tumors biopsy-proven or suspicious for malignancy were enrolled in an NIR imaging clinical trial. Patients received a range of ICG doses 1 day before surgery: 1 mg/kg (n = 8), 2 mg/kg (n = 8), 3 mg/kg (n = 13), 4 mg/kg (n = 8), and 5 mg/kg (n = 8). Intraoperatively, NIR imaging was performed. The endpoint was to identify the highest tumor-to-background fluorescence ratio (TBR) for each tumor type at each dose. Final pathology confirmed tumor histology.

Results: Of 45 patients, 41 had malignancies (18 non-small cell lung cancers [NSCLC], 3 pulmonary neuroendocrine tumors, 13 thoracic metastases, 4 thymomas, 3 mesotheliomas). At doses of 4 to 5 mg/kg, the TBR from primary NSCLC vs other malignancies was no different (2.70 vs 3.21, p = 1.00). At doses of 1 to 3 mg/kg, the TBR was greater for the NSCLCs (3.19 vs 1.49, p = 0.0006). Background fluorescence from the heart or ribs was observed in 1 of 16 cases at 1 to 2 mg/kg, 5 of 13 cases at 3 mg/kg, and 14 of 16 cases at 4 to 5 mg/kg; this was a major determinant of dose optimization.

Conclusions: This is the first study to demonstrate that the optimal NIR contrast agent dose varies by tumor histology. Lower dose ICG (2 to 3 mg/kg) is superior for nonprimary lung cancers, and high dose ICG (4 to 5 mg/kg) is superior for lung cancers. This will have major implications as more intraoperative imaging trials surface in other specialties, will significantly reduce costs and may facilitate wider application.

Trial registration: ClinicalTrials.gov NCT02640170.

Copyright © 2018 American College of Surgeons. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1.

(A) Percentage of fluorescent tumors and mean tumor-to-background ratio (TBR) of non-small cell lung cancer (NSCLC) and other malignant tumors at low (1–3 mg/kg) and high (45 mg/kg) ICG doses. (B) Representative preoperative computed tomography (CT), intraoperative white light, intraoperative near-infrared (NIR) overlay, and hematoxylin and eosin (H&E) (20x) images of a pulmonary nodule at each indocyanine green (ICG) dose in the dose de-escalation trial. Final pathology for each case was: 5 mg/kg – pulmonary adenocarcinoma, 4 mg/kg – adrenocortical carcinoma, 3 mg/kg – typical carcinoid, 2 mg/kg – colorectal adenocarcinoma, and 1 mg/kg – endometrial carcinoma.

Figure 2.

Representative case of specimen mapping for a pulmonary leiomyosarcoma metastasis. (A) Gross imaging. The tumor displayed in situ and ex vivo fluorescence. (B) Microscopic imaging. Near-infrared scanner and fluorescence microscopy (20x) images demonstrate more fluorescence in the tumor than in adjacent uninvolved lung.

Figure 3.

Specimen mapping from near-infrared (NIR) imaging of a pulmonary endometrial carcinoma metastasis. (A) Ex vivo white light, (B) ex vivo NIR, (C) white light bread loaf section of tumor, (D) NIR bread loaf section of tumor, (E) tumor section on NIR scanner, (F) hematoxylin and eosin (H&E) (20x) images. (G) Indocyanine green (ICG), (H) DAPI, and (I) ICG and DAPI overlay fluorescence microscopy (20x).

Figure 4.

(A) Mean fluorescence intensity (MFI) at each ICG dose. (B) Mean tumor-tobackground ratio at each ICG dose. (C) Percent of cases with background fluorescence in the heart and/or ribs at each indocyanine green (ICG) dose.

Figure 5.

Representative images from near-infrared (NIR) imaging of (A) pulmonary myxofibrosarcoma metastasis, (B) thymoma, and (C) mesothelioma 1 day after infusion of 3 mg/kg ICG in the validation cohort.