SU‐E‐J‐196: In‐Vivo Tumor Blood‐Oxygen Content Measurement via Interstitial Optical Transmission Spectroscopy

Purpose: To demonstrate the application of in‐vivo diffuse optical transmission spectroscopy in quantifying oxygen saturation in interstitial tissue, and to use this technique to examine reoxygenation dynamics in real‐time as tumors responds to radiotherapy. Methods: Two 200 micron core fiber optics were threaded through two 21 gauge hypodermic needles: one coupled to an OceanOptics QE65000 spectrometer, and the other to an Ocean Optics HL‐2000‐HP 20W light source. These needles were fixed approximately 3 mm apart, and inserted into nude mice with human head‐ and‐neck tumor xenografts. The oxygen saturation was then measured as a function of time after irradiation at intervals of 0.5, 1, 2, 6, 12, and 24, to measure the tumors' prompt oxygen saturation response to radiation. Results: Blood volume, deoxy and oxy‐hemoglobin concentrations were measured through least‐squares fitting of transmission spectra. Furthermore, various configurations of interstitial fiber optic probes were explored to optimize signal strength. Improvement of the optical coupling to the biological system and a concurrent increase in source intensity are the main two focuses for boosting signal strength. Conclusions: This work has the potential to give an understanding of the time‐scales of hypoxia and reoxygenation in vivo as tumors respond to radiation injury. This technique is of particular interest for hypofractionated therapies particularly treatments of only two or three treatments, where optimizing treatment timing can increase the tumorcidal effect of the remaining fractions.