INTERSTITIAL PHOTODYNAMIC THERAPY IN THE DUNNING R3327-AT6 PROSTATIC-CARCINOMA

Interstitial photodynamic therapy (PDT) could be an alternative radica l treatment for prostate cancer. The ability to predict the depth of n ecrosis is necessary for light treatment planning using multiple optic al fibres. The extent of PDT necrosis was studied in subcutaneously im planted R3327-AT6 Dunning prostate tumours which had similar optical c haracteristics to human prostate. Tumour-bearing subjects were given 2 0 mg kg(-1) Haematoporphyrin esters (HPE) and irradiated 24h later wit h 630 nm laser light. Five subjects per group were treated with increa sing light doses (50-450 J cm(-1)) delivered interstitially via a sing le 2 cm long cylindrical diffuser. After 450 J cm(-1) of irradiation, 4.3 +/- 0.8 cm(3) [standard error of the mean (s.e.m.)] of tumour tiss ue was necrosed to a depth of 10.5 +/- 0.8 mm around the diffuser. The re was an approximately linear correlation between the volume of PDT n ecrosis around the fibre and prescribed light dose. The mean threshold light dose for PDT effect was 18 +/- 2 J cm(-2). In this tumour with a mean photosensitizer concentration of 16 +/- 1.5 mu g g(-1), low lig ht doses produced tumour necrosis. PDT using multiple diffusers could destroy a relatively large tumour volume and the 'diffusion theory' mo del reliably predicted the depth of necrosis.