Room: Track 1
Purpose: The success of PDT depends on the accuracy of a prescribed light dose delivered to the tumor. Tissue optical properties are important to determine the light dose. We have developed a dual-channel continuous wave transmittance dosimetry system and algorithms for interstitial determination of optical properties (µa and µs’) in intracavitary and semi-infinite medium conditions. We developed an analytical expression to determine scatter light fluence rate measured in an enclosed cylindrical geometry to the surrounding tissue optical properties in tissue-simulating liquid phantoms. In addition, the accuracy of determining tissue optical properties using the model was evaluated by comparing the recovered optical properties to the known optical properties of a series of independent test phantoms.
Methods: Two parallel catheters were placed 5 mm apart. One held a point light source and the other held an isotropic detector, the latter of which is scanned along the length of the light source-containing catheter using a stepper motor. 14 phantoms of known optical properties, with the absorption coefficient (µa) ranging from 0.1-0.9 1/cm and the scattering coefficient (µs’) ranging from 6.7-20 1/cm. Further validation of scatter light fluence rate on the surface of the cylindrical geometry and the optical properties is performed using Monte Carlo simulation (MCX-CL), an OpenCL-based Monte Carlo simulator for photon transport modeling.
Results: An analytical model was derived that relates scattered light fluence rate measured in an enclosed cylindrical geometry to the surrounding tissue optical properties in tissue-simulating liquid phantoms. The percent error for determining µa and µs’ from a set of test phantoms is found to be <10%. MC simulation confirms that the scattered light comes mostly from tissue near by the point source.
Conclusion: The study demonstrated the feasibility of determining the tissue optical properties in anal PDT using a two-catheter method using a point source.
Funding Support, Disclosures, and Conflict of Interest: The authors Timothy Zhu and Theresa Busch declare consultant role in Simphotek Inc. Other authors declare no financial COI. The authors would like to acknowledge funding support from National Cancer Institute: R21CA223366.