A Comparison of Multichannel Singlet Oxygen Luminescence Dosimetry (MSOLD) and Singlet Oxygen Explicit Dosimetry (SOED)

Direct detection of singlet-state oxygen ([1O2]) is a crucial objective in type II photodynamic therapy (PDT), achievable through the implementation of multispectral singlet oxygen dosimetry (MSOLD). To accurately assess the amount of reactive singlet oxygen, the Singlet Oxygen Explicit Dosimetry (SOED) model was developed, incorporating parameters such as light fluence rate, photosensitizer concentration, and ground-state oxygen concentration. This study focuses on comparing the results obtained from MSOLD and SOED by measuring the singlet oxygen signal via a commercial InGaAs spectrometer and subsequently calculating reactive singlet oxygen based on the SOED theory. A continuous-wave laser emitting at 630 nm is employed to excite Protoporphyrin IX (PPIX) in methanol, varying the concentration from 10 mg/kg to 100 mg/kg. Utilizing the Singular Value Decomposition (SVD) algorithm, the measured singlet oxygen spectrum is fitted to extract the singlet oxygen signal. To simulate clinical PDT scenarios, real-time singlet oxygen spectra are collected over 1200 seconds, employing a 1.5 mm diameter optic fiber for signal collection. Groundstate oxygen concentration is measured using a commercial oxygen probe while the laser is inactive, and photosensitizer concentration is assessed via a custom-made contact probe. Additionally, the fluence rate of the laser is measured using an isotropic detector. The Reactive Singlet Oxygen is then calculated using the SOED model, incorporating the photosensitizer concentration, oxygen concentration, and photon fluence rate. Detailed comparisons between MSOLD and SOED results are presented, offering valuable insights into the accuracy and reliability of both methods in quantifying singlet-state oxygen during PDT.