Photodynamic therapy for localised prostatic cancer: light penetration in the human prostate gland

We are investigating the feasibility of photodynamic therapy in the treatment of localised prostatic cancer. Of major importance in this form of treatment is the extent to which light penetrates the target organ; hence, our interest in the optical properties of the human prostate gland. We obtained three whole prostates from autopsies of patients who died of non-urological causes. Red light was launched interstitially and detector fibres measured light intensity as a function of distance from the delivery fibre end. The optical constants derived from the three prostates were almost identical and indicated that light was predominantly scattered rather than absorbed (mean absorption and scattering coefficients 0.07 +/- 0.02 mm.-1 and 0.86 +/- 0.05 mm.-1 respectively). In a comparison of the tissue penetration by four different wavelengths, 633 nm red light was found to be transmitted best. Light propagation in the heavily absorbing tissue of the human liver was 4.3 times poorer than in the prostate. Such a combination of low absorption and high scattering characteristics in prostatic tissue would enhance the effectiveness of PDT. The optical constants derived will enable "light treatment planning" in patients with prostatic cancer.