A mathematical model for light dosimetry in photodynamic destruction of human endometrium

Abstract

Abstract. 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 paper, we analyse light propagation through the uterus in order to specify the requirements for a light delivery system capable of effectively performing endometrial PDT. Our approach involves developing an analytical model based on diffusion theory to predict optical fluence rate distributions when cylindrical and spherical optical applicators are placed in the uterine cavity. We apply the results of our model calculations to estimate the thermal effects of optical irradiation and the effective photodynamic optical dose. Theoretical fluence rate calculations 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 entire endometrium. When the optical power per unit length of each cylindrical applicator is 100 mW cm −1 (at 630 nm), a fluence rate of 40 mW cm −2 is delivered to the boundary layer between the endometrium and the 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 level that is generally accepted to cause tissue damage throughout the endometrium in most patients.

Intrauterine light delivery for photodynamic therapy of the human endometrium

“…The post-menopausal uteri weighed 71 ± 21 g, with a transverse diameter of the uterine cavity ranging from 28 to 56 mm (40 ± 6). Histology revealed that six of Svaasand (1984) and Tromberg et al (1995). A total of 10 pre-menopausal and four post-menopausal patients were studied.…”

“…However, optical irradiation will initiate a temperature rise in the tissue. To minimize the thermal effects of irradiation, the power coupled into a cylindrical light applicator should not exceed 100 mW/cm fibre length (Svaasand, 1984;Tromberg et al, 1995). On the other hand, to be clinically acceptable, treatment times should be kept short, e.g.…”

“…The optical penetration depth is defined as the distance from the surface of the tissue at which the fluence rate drops to 37% of its initial value . The calculation of the penetration depth from the measured fluence rates at different source detector separations has been described elsewhere (Svaasand, 1984;Tromberg et al, 1995). If fibroids were visible macroscopically, the measurements were made in tissue which appeared to be normal.…”

Performance evaluation of cylindrical fiber optic light diffusers for biomedical applications

“…Star et al [7] have noted large spatial variances during irradiation of the bladder, and van Veen et al [8] demonstrated similar effects in the esophagus. These problems have led to the development of specialty applicators such as for the uterus [9], the esophagus [10,11] and post resection cavities in the brain [12].…”

Role of Photodynamic Therapy in the Management of Gastrointestinal Cancer

“…Apart from its use in the treatment of gastrointestinal tumours, PDT has been used in the treatment of malignancies in the brain [35], skin [36], ovaries [37], uterus [38], lungs [39], and oral cavity [40]for more than a decade. More recently, there has been considerable interest in the use of this therapy in the management of Barrett’s oesophagus [41, 42, 43]and intimal hyperplasia of peripheral arteries [44].…”