AbstractID: 6933 Title: Interstitial light distribution at 730nm prostate photodynamic therapy Light distribution in tissue is important for dosimetry of prostate photodynamic therapy (PDT). In this study we measured the light fluence distribution for 730-nm in optical phantoms. A 0.3-mm diameter isotropic detector with scattering tip was used to measure the light fluence rate. Two different type of phantoms were used to simulate prostates: liquid phantoms composed of intralipid and green ink and solid prostate shaped phantoms made of silicon gel with TiO2 and C mixture. The light sources used were point and linear sources. We used three different absorption coefficients (.01, .03 and .05 cm-1), and two scattering coefficients (5 and 10 cm-1). We found that µa is proportional to the concentration of green ink with the proportionality constant equal to 7.182 and µs is proportional to the concentration of intralipid with the proportionality constant equal to 2092. When using the point source, the fluence rate agrees with the diffusion approximation equation: φ=sµeff2 e-µeff r/4πµar , where µa and µeff are the absorption and the effective coefficients and s is the total power of the point source. The light fluence for the linear source agrees with the diffusion approximation, provided the light power density distribution of the linear fiber is individually optimized. In conclusion, we have a realistic knowledge about what is the light fluence distribution inside the prostate, information that can be used to quantitatively estimate light fluence distribution for prostate PDT.