INTERSTITIAL PHOTODYNAMIC THERAPY IN THE CANINE PROSTATE

Objective To determine the depth of tissue destruction and the minimum light dose required for necrosis in interstitial photodynamic therapy (PDT), as a prerequisite for the investigational therapy of patients. Materials and methods Seven adult beagle dogs were given 2 mg/kg of t he photosensitizer Photofrin(TM) intravenously and two controls receiv ed none, After 24 h, 450 J/cm of 630 nm wavelength laser light was del ivered interstitially to the prostate via a 2 cm long diffuser fibre. Seven single-fibre treatments were performed in five sensitized dogs a nd two single-fibre treatments in the controls, The two remaining sens itized dogs had two fibres placed 10 mm apart within the prostate to d etermine the coalescence of PDT lesions, The penetration depth of ligh t was measured in all prostates, and after PDT the extent of necrosis was assessed histologically. Results The mean (standard deviation, SD) radius of PDT destruction around each diffuser was 5.3 (1.4) mm and P DT lesions overlapped in prostates treated with two fibres placed 10 m m apart, There was no observable tissue damage in the controls, The me an (so) minimum light dose required for PDT necrosis was 84 (64) J/cm( 2), Differences among animals in the light penetration depth were smal l, with a mean of 2.14 (0.2) mm, and did not correlate with the depth of necrosis (P=0.07). Bleeding around the optical diffuser fibre imped ed light penetration. Conclusion Interstitial PDT in the canine prosta te using Photofrin(TM) produced modest volumes of tissue necrosis. The minimum light dose required to induce necrosis was variable because b leeding was unpredictable in relation to the optical fibre.