MUCOSAL ABLATION USING PHOTODYNAMIC THERAPY FOR THE TREATMENT OF DYSPLASIA - AN EXPERIMENTAL-STUDY IN THE NORMAL RAT STOMACH

Surgery is the only effective treatment for dysplasia in the gastroint estinal tract with considerable associated morbidity and mortality and is difficult to justify without confirmed malignancy. Photodynamic th erapy (PDT) produces localised necrosis, which can be limited to the m ucosa. This study examined the mechanical properties of the normal rat stomach after PDT. The aim of this study was to measure the bursting pressure of PDT lesions in the stomach and to assess gastric emptying after producing circumferential mucosal necrosis at the pylorus by PDT . Two photosensitising agents were used 5-aminolaevulinic acid (ALA), and aluminium disulphonated phthalocyanine (AlS(2)Pc). Normal rats wer e sensitised and PDT lesions created in the stomach with red light. Th e bursting pressure was measured and compared with that in thermal con trol lesions. In further experiments, circumferential mucosal necrosis was produced at the pylorus, and animals observed for subsequent eati ng and weight gain. It was found that gastric bursting pressure was re duced after thermal injury, but not at any time after PDT (with AlS(2) Pc, but not ALA, adhesive omental reinforcement was required to mainta in the gastric wall strength at one week). For the pyloric lesions, ga stric emptying was permanently impaired using AlS(2)Pc, but with low d ose ALA (20 mg/kg) had returned to normal by three days. With ALA, but not AlS(2)Pc, necrosis could be Limited to the mucosa. In conclusion, using ALA, selective ablation of the gastric mucosa is possible, whic h does not reduce the strength of the stomach and only temporarily del ays gastric emptying. PDT is a promising technique for the circumferen tial ablation of dysplastic mucosa.