Tissue-simulating Phantoms for Assessing Potential Near-infrared Fluorescence Imaging Applications in Breast Cancer Surgery

Summary

Near-infrared fluorescence (NIRF) imaging may improve therapeutic outcome of breast cancer surgery by enabling intraoperative tumor localization and evaluation of surgical margin status. Using tissue-simulating breast phantoms containing fluorescent tumor-simulating inclusions, potential clinical applications of NIRF imaging in breast cancer patients can be assessed for standardization and training purposes.

Abstract

Inaccuracies in intraoperative tumor localization and evaluation of surgical margin status result in suboptimal outcome of breast-conserving surgery (BCS). Optical imaging, in particular near-infrared fluorescence (NIRF) imaging, might reduce the frequency of positive surgical margins following BCS by providing the surgeon with a tool for pre- and intraoperative tumor localization in real-time. In the current study, the potential of NIRF-guided BCS is evaluated using tissue-simulating breast phantoms for reasons of standardization and training purposes.

Breast phantoms with optical characteristics comparable to those of normal breast tissue were used to simulate breast conserving surgery. Tumor-simulating inclusions containing the fluorescent dye indocyanine green (ICG) were incorporated in the phantoms at predefined locations and imaged for pre- and intraoperative tumor localization, real-time NIRF-guided tumor resection, NIRF-guided evaluation on the extent of surgery, and postoperative assessment of surgical margins. A customized NIRF camera was used as a clinical prototype for imaging purposes.

Breast phantoms containing tumor-simulating inclusions offer a simple, inexpensive, and versatile tool to simulate and evaluate intraoperative tumor imaging. The gelatinous phantoms have elastic properties similar to human tissue and can be cut using conventional surgical instruments. Moreover, the phantoms contain hemoglobin and intralipid for mimicking absorption and scattering of photons, respectively, creating uniform optical properties similar to human breast tissue. The main drawback of NIRF imaging is the limited penetration depth of photons when propagating through tissue, which hinders (noninvasive) imaging of deep-seated tumors with epi-illumination strategies.

Introduction

Breast-conserving surgery (BCS) followed by radiotherapy is the standard treatment for breast cancer patients with T₁-T₂ breast carcinoma^1,2. Inaccuracies in intraoperative assessment of the extent of surgery result in positive surgical margins in 20 to 40% of the patients who underwent BCS, necessitating additional surgical intervention or radiotherapy^3,4,5. Although extensive resection of adjacent healthy breast tissue might reduce the frequency of positive surgical margins, this will also hamper cosmetic outcome and increase comorbidity^6,7. Novel techniques are therefore needed that provide intraoperative feedb....

Protocol

1. Create Silicone Molds for Tumor-simulating Inclusions

1. Collect solid items of the desired shape and size that can serve as models for tumor-simulating inclusions, e.g., beads or marbles.
2. Thoroughly clean the tumor models. To ensure an easy removal from the silicone mold, the tumor models can be sprayed with anti-stick spray or covered with a thin layer of petroleum jelly or beeswax.
3. Place each model in a separate thin walled square (plastic) box with a smooth surface. If necessary, fixate the model to the bottom of the box to keep it in position. Use a box that is slightly bigger than the tumor model itself to avoid wasting e....

Results

Results from this study have been previously reported elsewhere⁹.

Our data show that NIRF imaging can be applied to detect fluorescent tumor-simulating inclusions in tissue-simulating breast phantoms, simulating NIRF-guided breast-conserving surgery in breast cancer patients. Using our phantom model, we found intraoperative tumor localization, NIRF-guided tumor resection, intraoperative assessment of surgical cavity margins, and detection of residual disease to be feasible (.......

Discussion

We simulated potential clinical applications of NIRF-guided BCS through the use of breast-shaped phantoms with integrated tumor-simulating inclusions. Intraoperative tumor localization, NIRF-guided tumor resection, evaluation on the extent of surgery, and postoperative assessment of surgical margins were all found feasible using a custom-build NIRF camera system. Noninvasive detection of fluorescent tumor-simulating inclusions was only feasible for inclusions positioned in the phantom tissue at a depth of 2 cm or less. I.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Bovine hemoglobin	Sigma-Aldrich, Zwijndrecht, The Netherlands	H2500	Simulates absorption of photons in tissue
Intralipid 20%	Sigma-Aldrich, Zwijndrecht, The Netherlands	I141	Simulates scattering of photons in tissue
Silicone A translucent 40 (2-components poly-addition silicone)	NedForm, Geleen, The Netherlands		Package consists of components A and B, that should be mixed one on one (A:B=10:1).  Link to manufacturers page: http://tinyurl.com/ncjq7jx
Gelatine 250 Bloom	Sigma-Aldrich, Zwijndrecht, The Netherlands	48724	Construction of breast-shaped phantoms
Agarose	Hispanagar, Burgos, Spain		Construction of tumor-simulating inclusions
Tris	Sigma-Aldrich, Zwijndrecht, The Netherlands	T1503
HCl	Sigma-Aldrich, Zwijndrecht, The Netherlands	258148
NaCl	Sigma-Aldrich, Zwijndrecht, The Netherlands	S9888
NaN3	Merck, Darmstadt, Germany	822335	CAUTION: severe poison. The toxicity of this compound is comparable to that of soluble alkali cyanides and the lethal dose for an adult human is about 0.7 grams.
Examples of NIRF imaging devices for intraoperative application:
T2 NIRF imaging platform	SurgVision BV, Heerenveen, The Netherlands		Customized NIRF imaging system used in the current study. More details available at www.surgvision.com
Photodynamic Eye	Hamamatsu Photonics Deutschland GmbH, Herrsching am Ammersee, Germany	PC6100	www.iht-ltd.com
FLARE imaging system kit	The FLARE Foundation Inc, Wayland, MA, USA		www.theflarefoundation.org
Fluobeam	Fluoptics, Grenoble, France		www.fluoptics.com
Artemis handheld camera	Quest Medical Imaging BV, Middenmeer, the Netherlands		www.quest-mi.com
Examples of NIRF fluorescent dyes for intraoperative application:
Indocyanine green	ICG-PULSION,  Feldkirchen, Germany	PICG0025DE	Clinical grade fluorescent dye for NIRF imaging used in the current study. More details available at www.pulsion.com
IRDye 800CW NHS Ester	LI-COR Biosciences, Lincoln, NE, USA	929-70021	www.licor.com