Temperature monitoring during photodynamic therapy of skin tumors with topical 5-aminolevulinic acid application

Temperature monitoring during photodynamic therapy (PDT) with topical 5-aminolevulinic acid (ALA) cream application was performed on 22 patients with solar keratoses (SK) and basal cell carcinoma (BCC). The lesions were located on the forehead, nose, ear and cheek. Temperature measurements during photoirradiation, with a power density of 100 mW/cm² from an incoherent light source (light delivery system for PDT), were carried out by noncontact (infrared thermal imaging radiometer) and contact (thermocouple) methods. Thermal imaging analysis revealed nonuniform temperature distribution in the irradiated areas. The temperature gradually increased from the peripheral to the central zone of the area. The results showed that photoirradiation induced heating of the skin tumors to 39.5-42.5 °C during the PDT procedure. The temperature of normal skin areas disposed symmetrically to the lesions on the contralateral side at the same conditions of irradiation (without prior ALA application) was about 42-43.5 °C. The surface temperature differences (ΔT) between the normal and tumor tissues after 10 min of irradiation were 3.3 ± 0.5 °C in the forehead areas, 2.5 ± 0.4 °C in the nose areas and 0.8 ± 0.3 °C in the ear areas.