Exploitation of interstitial brachytherapy techniques for photodynamic therapy--I. Treatment planning for interstitial photoexcitation therapy: a photodosimetry treatment planning system

摘要

Abstract: A photodosimetry computer program, T-PIPET, was developed to rapidly compute maps of relative light intensity within tumors illuminated by implanted optical fibers. Light attenuation was measured along radial tracks from laterally-diffusing fibers implanted into both the R3327-AT and R3327-H Dunning rat prostate carcinomas and input to the computer program. The calculations assumed (1) uniform optical property of tissue through the tumor, (2) uniform and equal illuminance from the length of optical diffuser and between fibers and (3) precise needle implantation. Values of relative light intensity were computed, color-coded and imaged for a 5 $MUL 5 cm tumor cross section (a 150 $MUL 150 pixel array). Illuminators consisting of seven laterally-diffusing fibers implanted as six adjacent equilateral triangles were tested. The uniformity of light fields within encompassed tumor volumes was determined as a function of fiber spacing. Measures of light intensity along specific tracks within tumors agreed well ($POM 10%) with values of relative light intensity predicted by T-PIPET. The rapid falloff of light dose beyond the illuminator will assist in minimizing normal tissue damage outside the tumor volume. To cure slid tumors, a specific light dose must be delivered throughout the tumor volume and recurrence might be expected from tumor zones which are underdosed. A 9-fiber illuminator has been constructed to deliver light more uniformly to the tumor periphery. These illuminators have been tested with R3327-AT tumors illuminated with 673 nm light after i.v. administration of a pheophorbide-base photosensitizer. !14