In vivo measurement of the optical interaction coefficients of human tumours at 630 nm

Abstract

The light distribution within a treatment volume is determined by the source geometry (e.g. superficial or interstitial illumination) and the optical interaction coefficients of the irradiated tissue. The authors have measured the energy fluence rate at various points within tumours undergoing irradiation with 630 nm light for photodynamic therapy for several source geometries. The relative positions of source and detector fibres were determined using CT scanning techniques. The results of the measurements were then applied to solutions of the diffusion theory which allowed the determination of the absorption coefficient ( Sigma _a=30.5+or-16 m^-1), the reduced scattering coefficient ( Sigma _s=941+or-735 m^-1), the effective attenuation coefficient ( Sigma _eff=261+or-49 m^-1) and the build-up coefficient which relates surface irradiance to the energy fluence rate at depth (k=1.6+or-0.6).