Photoacoustic imaging of sentinel lymph nodes, a feasibility study

The global impact of cancer as a leading cause of death and underscores the
significance of accurate staging, prognostic stratification, and treatment
planning, particularly in cases of distant metastasis. Sentinel lymph node
biopsy (SLNB) plays a crucial role in these processes for breast cancer and
melanoma patients. The conventional method, using technetium and blue dye, has
drawbacks such as radiation exposure and logistical challenges.

Optical imaging techniques, specifically fluorescent light imaging (FLI) with
near-infrared (NIR) cameras using indocyanine green (ICG), offer a non-invasive
alternative. However, their limitations, including a low detection rate through
the skin, necessitate exploration of novel technologies. Photoacoustic imaging
(PAI) emerges as a potential solution, providing advantages like no radiation
exposure, portability, and real-time high-resolution imaging. PAI utilizes the
optical absorption properties of ICG to generate acoustic waves for
reconstructing three-dimensional images of sentinel lymph nodes (SLNs).

Two PAI configurations, laser-based and LED-based, are available. Laser-based
systems offer deeper tissue penetration and a broad spectrum of wavelengths,
potentially aiding in tissue differentiation and cancer detection. However,
they require a controlled environment and safety measures. LED-based systems
address safety concerns but have limited penetration depth. The study aims to
investigate the clinical viability of ICG-mediated photoacoustic imaging for
SLNs using both LED-based and laser-based PAI systems, with the goal of
improving SLN mapping accuracy and reducing reliance on technetium.

Primary Objective:
• To investigate the feasibility of utilizing PAI as a means of detecting the
SLN in patients with melanoma or breast cancer

Secondary Objective(s):
• Determine the most effective wavelengths for detecting ICG in PAI
• Investigate the optimal ICG dosage and time interval between imaging and
injection of ICG in PAI
• Find the maximum depth at which the SLN can be detected using PAI
• Explore the identification of melanoma metastases in the SLN

This study is a prospective feasibility study initiated by the researchers,
focusing on the detection of the SLN using PAI. The research consisted of two
distinct phases, namely phase 1 involving the participation of volunteers, and
phase 2 involving patients with melanoma or breast cancer.

Participation takes ~45 minutes of a volunteer*s/patient*s time. For patients,
imaging will take place at the same day of the SLNB, so no extra travel time is
needed for the patients. During this study an extra ICG injection will be
administrated. The risks of side effects will be minimal. Possible side effects
will be, among others, hypersensitivity reactions. For this reason, we excluded
patients known with clinically significant allergy or anaphylactic reactions to
any of the components of the agent, including iodine. In addition,
precautionary measures were taken, including supervised administration by
qualified staff and availability of adequate medications in case of a
hypersensitivity reaction.
Furthermore the SLNs will be imaged with two PAI systems (LED-based and
laser-based). The imaging itself is not uncomfortable and comparable to regular
ultrasound imaging. The residual risks associated with this study are
negligible, given the utilization by trained researchers and the implementation
of laser safety measures.
Regardless of the findings, the surgical plan will not be altered and therefore
the patient risks are minimal, The participants will not have a direct benefit
from participating, but this research contributes to potentially improve SLN
mapping.