A MATHEMATICAL-MODEL FOR LIGHT DOSIMETRY IN PHOTODYNAMIC DESTRUCTION OF HUMAN ENDOMETRIUM

We are involved in the development of photodynamic therapy (PDT) as a minimally invasive method for treating dysfunctional uterine bleeding, one of the primary clinical indications for hysterectomy. In this pap er, we analyse light propagation through the uterus in order to specif y the requirements for a light delivery system capable of effectively performing endometrial PDT. Our approach involves developing an analyt ical model based on diffusion theory to predict optical fluence rate d istributions when cylindrical and spherical optical applicators are pl aced in the uterine cavity. We apply the results of our model calculat ions to estimate the thermal effects of optical irradiation and the ef fective photodynamic optical dose. Theoretical fluence rate calculatio ns are compared to fluence rate measurements made in fresh, surgically removed human uteri. Our results show that a trifurcated cylindrical optical applicator inserted into the human uterus can provide a light dose that is sufficient to cause photodynamic destruction of the entir e endometrium. When the optical power per unit length of each cylindri cal applicator is 100 mW cm(-1) (at 630 nm), a fluence rate of 40 mW c m(-2) is delivered to the boundary layer between the endometrium and t he myometrium (a depth of about 4-6 mm). The optical fluence delivered to the boundary layer after 20 min of exposure is 50 J cm(-2), a leve l that is generally accepted to cause tissue damage throughout the end ometrium in most patients.