Laser photothermal effects on tumor vasculature using laser Doppler flowmetry

Laser Doppler perfusion monitors have been used to study blood flow in tissue. They are useful tools to understand and monitor vascular changes during the treatment of lesions. In addition, lasers have been used in the treatment of cancers through photothermal and photochemical interactions, and the effects of laser treatment in many cases depend on the vasculature of the tumors and their surrounding tissue. In this study, an 805-nm laser was used to non-invasively irradiate subcutaneous mammary and prostatic tumors in rats. The perfusions on the tumor surface, the overlying skin, and underlying muscle tissues were measured using laser Doppler flowmetry during the near-infrared laser treatment. The perfusion probe was fitted into a 16-gauge needle so that the probe could be inserted into the target tissue for the perfusion measurement. The perfusion on the surface of the tumor decreased at the beginning of the laser irradiation, followed by a significant increase. Then, the perfusion was decreased again to a pre-treatment level. The perfusion of the skin tissue and muscle tissue, however, remained relatively unchanged during laser irradiation. Our experimental results indicate that laser photothermal effects could be monitored by the laser Doppler flowmetry and that tumor vascular information could be used to improve the effectiveness of the laser treatment of cancer.