Interstitial photodynamic therapy for primary prostate cancer incorporating realtime treatment dosimetry

Photodynamic therapy (PDT) for the treatment of prostate cancer has been demonstrated to be a safe treatment option capable of inducing tissue necrosis and decrease in prostate specific antigen (PSA). Research groups report on large variations in treatment response, possibly due to biological variations in tissue composition and shortterm response to the therapeutic irradiation. Within our group, an instrument for interstitial PDT on prostate tissue that incorporates realtime treatment feedback is being developed. The treatment protocol consists of two parts. The first part incorporates the pre-treatment plan with ultrasound investigations, providing the geometry for the prostate gland and surrounding risk organs, an iterative random-search algorithm to determine near-optimal fiber positions within the reconstructed geometry and a Block-Cimmino optimization algorithm for predicting individual fiber irradiation times. During the second part, the therapeutic light delivery is combined with measurements of the light transmission signals between the optical fibers, thus monitoring the tissue effective attenuation coefficient by means of spatially resolved spectroscopy. These data are then used as input for repeated runs of the Block-Cimmino optimization algorithm. Thus, the irradiation times for individual fibers are updated throughout the treatment in order to compensate for the influence of changes in tissue composition on the light distribution at the therapeutic wavelength.