Optical properties of adenocarcinoma and squamous cell carcinoma of the gastroesophageal junction

Abstract

Photodynamic therapy (PDT) is an alternative to radical surgical resection for T1a or nonresectable carcinomas of the gastroesophageal junction. Besides the concentration of the photosensitizer, the light distribution in tissue is responsible for tumor destruction. For this reason, knowledge about the behavior of light in healthy and dysplastic tissue is of great interest for careful irradiation scheduling. The aim of this study is to determine the optical parameters (OP) of healthy and carcinomatous tissue of the gastroesophageal junction in vitro to provide reproducible parameters for optimal dosimetry when applying PDT. A total of 36 tissue samples [adenocarcinoma tissue (n=21), squamous cell tissue (n=15)] are obtained from patients with carcinomas of the gastroesophageal junction. The optical parameters are measured in 10-nm steps using new integrating sphere spectrometers in the PDT-relevant wavelength range of 300 to 1140 nm and evaluated by inverse Monte-Carlo simulation. Additional examinations are done in healthy tissue from the surgical safety margin. In the wavelength range of frequently applied photosensitizers at 330, 630, and 650 nm, the absorption coefficient in tumor tissue (adenocarcinoma 1.22, 0.16, and 0.15 mm(-1); squamous cell carcinoma 1.48, 0.13, and 0.11 mm(-1)) is significantly lower than in healthy tissue (stomach 3.34, 0.26, and 0.20 mm(-1); esophagus 2.47, 0.21, and 0.18 mm(-1)). The scattering coefficient of all tissues decreases continuously with increasing wavelength (adenocarcinoma 22.8, 12.99, and 12.52 mm(-1); squamous cell carcinoma 19.44, 9.35, and 8.98 mm(-1); stomach 20.55, 13.96, and 13.94 mm(-1); esophagus 20.34, 12.56, and 12.22 mm(-1). All tissues show an anisotropy factor between 0.80 and 0.94 over the entire spectrum. The maximum optical penetration depth for all tissues is achieved in the range of 800 to 1100 nm. At the wavelength range of 330, 630, and 650 nm, the optical penetration depth is significantly higher in carcinoma tissue (adenocarcinoma 0.27, 1.54, and 1.66 mm; squamous cell carcinoma 0.23, 1.71, and 1.84 mm) than in healthy tissue (stomach 0.16, 1.10, and 1.26 mm; esophagus 0.17, 1.47, and 1.65 mm; p<0.05). Above 1000 nm, a higher absorption coefficient of tumor tissue results in a lower optical penetration depth than in healthy tissue (p<0.05). The higher absorption and scattering of the tumor tissue in the wavelength range of available photosensitizer is associated with a low optical penetration depth. This necessitates higher energy doses and long application times or repeated applications to effectively treat large tumor volumes. Photosensitizers optimized for larger wavelength range need to be developed to increase the efficacy of PDT.

Measurement of optical properties of pig esophagus by using a modified spectrometer set‐up

“…The reason for the difference of the oxy-hemoglobin peak found in this study but not found by Holmer et al [8] can be partly caused by the lower wavelength resolution Holmer et al [8] used (10 nm). Moreover, it should also be noted that Holmer et al [8] measured human esophagus and in this study pig esophagus is used. A further indication that the usage of pig esophagus might lead to different measured absorption coefficient can be found by comparing the results of this study with the newer results of Jones et al [7] where they measured the optical properties of pig esophagus.…”

“…They also measured a higher absorption coefficient in the blue region and the region of the blood peaks. This difference is caused by the storage time of the sample in this study while Holmer et al [8] used fresh puré ed samples, the samples in this study had to be stored for few hours before they could be measured. The reason for the difference of the oxy-hemoglobin peak found in this study but not found by Holmer et al [8] can be partly caused by the lower wavelength resolution Holmer et al [8] used (10 nm).…”

“…This difference is caused by the storage time of the sample in this study while Holmer et al [8] used fresh puré ed samples, the samples in this study had to be stored for few hours before they could be measured. The reason for the difference of the oxy-hemoglobin peak found in this study but not found by Holmer et al [8] can be partly caused by the lower wavelength resolution Holmer et al [8] used (10 nm). Moreover, it should also be noted that Holmer et al [8] measured human esophagus and in this study pig esophagus is used.…”

“…The state of the art for ex-vivo samples is to use either Inverse-Adding-Doubling (IAD) [13,14] or Inverse-Monte-Carlo Simulations (IMCS) [8] to determine the optical properties. While Jones et al [1,7] used IAD to determine the optical properties of pig esophagus, Holmer et al [8] used IMCS.…”

“…While Jones et al [1,7] used IAD to determine the optical properties of pig esophagus, Holmer et al [8] used IMCS. However, Jones et al did not determine the g-factor.…”