Tumour vessel damage resulting from laser-induced hyperthermia alone and in combination with photodynamic therapy

This study examined tumour vessel injury resulting from laser-induced hyperthermia alone and in combination with photodynamic therapy (PDT) in the treatment of rat liver tumours by means of scanning electron microscopy. A total of 18 Wistar rats were divided into three groups. Group I (six animals) underwent hyperthermia for 15 min (15-min hyperthermia). Group II (six animals) underwent hyperthermia for 30 min (30-min hyperthermia). Group III (six animals) received the combined treatment of PDT and 30-min hyperthermia. For PDT, δ-amino laevulinic acid at a dose of 60 mg/kg of body weight was intravenously administered 60 min before irradiation at 635 nm. The morphological results indicated that 15-min hyperthermia gave rise to an increase in permeability of the vessels in the treated tumour. Thirty-min hyperthermia caused extreme oedema of vascular endothelial cells and restrictive openings of tumour branch vessels. The combined therapy of PDT and hyperthermia destroyed tumour vasculature. Large breaks of the inner wall of the treated tumour vessels were deeply involved in the basement membrane of the vessel. The results indicate that there may be a close link between inhibition of tumour growth and degree of damage to tumour vessels.