Exhibit Hall | Forum 9
Purpose: For type II photodynamic therapy (PDT), singlet oxygen, the dominant cytotoxic agent to kill tumors, can be directly quantified by multispectral singlet oxygen luminescence dosimetry (MSOLD). However, in-vivo MSOLD has proven to be a challenge due to the extremely weak, short-lived nature of the singlet oxygen phosphorescence signal. This study examines methods for optimizing MSOLD signal acquisition
Methods: Photofrin with various concentrations in MeOH or tissue-simulating liquid phantoms made of ink and intralipid solutions are used in the study. Two signal acquisition setups were tested: a setup using a dichroic mirror filter as a means of separating the treatment light and the singlet oxygen signal, and a fiber optic acquisition setup. The signal was filtered using a long pass filter, and spectral emission measurements were taken at 1200 nm, 1240 nm, 1250 nm, 1270 nm, and 1300 nm. We fit to the background using the 1200 nm, 1240 nm, and 1300 nm signals. A gaussian-fit was established for the background-subtracted 1270 nm singlet oxygen emission signal. Each setup was validated against singlet oxygen explicit dosimetry (SOED), which is based on explicit measurements of light fluence, oxygen concentration, and Photofrin concentration along with a suitable model.
Results: Both methods exhibit good correlation with SOED. The fiber optic setup shows stronger signal acquisition compared to the dichroic mirror setup, likely due to the reduced amount of spectral filtering components that compound signal loss. This resulted in better signal differentiation between different concentrations of photofrin in tissue-simulating liquid phantoms.
Conclusion: Both dichroic and fiber optic signal acquisition setups show promise for use as a method of direct dosimetry for PDT. However, the fiber optic acquisition method shows more robust signal differentiation, as well as better clinical viability due its compact setup and ease of use during clinical treatments. In-vivo application of MSOLD in a mouse model will be explored.
Funding Support, Disclosures, and Conflict of Interest: NIH R01BE028778, P01CA87971