Assessment Skin Cancer Margins Using Raman Spectroscopy
Abstract
Purpose
The fundamental objective is to determine extent of microscopic tumor infiltration into normal skin tissue to accurately define skin cancer brachytherapy margins.
Methods
Three subjects with biopsy-proven basal or squamous cell carcinoma were enrolled for clinical trial under IRB2023-00602. Spectra were acquired using a handheld Raman probe (EmVision) and spectroscope (Hubner Photonics Inc) using 785nm wavelength and 25 mW power. Measurements were taken of malignant lesions and surrounding skin at predefined grid spacing (5 mm). Data were labeled as normal appearing skin, lesion border and lesion by radiation oncologist visual assessment. Each Raman spectrum underwent baseline correction and median filtering to remove cosmic ray artifacts. Noise smoothing was performed using a Savitzky-Golay filter, and each spectrum was normalized to a range of 0 to 1. Spectra were averaged to observe peak differences of tissue classes. Intensity heat maps were generated for specific peaks, based on the literature and observations from our data.
Results
Relative to normal appearing tissue, tumors had increased peaks of DNA (~700 cm-1), phenylalanine (~1100cm-1), lipid (~1000, 1300, 1700cm-1), amide (~1200, 1600cm-1) and tryptophan (~700cm-1) and decrease in peak collagen (~900cm-1). In analysis of heat maps for the peaks mentioned above, there was an asymmetric intensity gradient when moving lateral from the lesion in different directions, indicating possible nonsymmetric infiltration of the cancer into adjacent tissue. Moreover, intensity heat maps demonstrated increased signal intensity toward the center of the visible tumors, which is consistent with expectations.
Conclusion
There is no reliable tool in our clinical practice that can provide in-vivo, real-time guidance to determine the margins of skin cancer for brachytherapy. Raman spectroscopy showed differential signal intensity between the tumor and adjacent normal tissue. It has potential to estimate the accurate extent of microscopic infiltrating tumor and guide skin cancer brachytherapy with informed margin assessment.