Dual thermal therapeutic method for selective treatment of deep-lying tissue

Photothermal therapy is based on converting laser radiation into heat due to the absorption of photons in tissue chromophores. The main advantage of the photothermal therapy is the capability of the wavelength-dependent selective therapy of abnormal tissue. However, this method has a drawback of the limitation of penetration depth of the incident laser radiation in the tissue, which depends on the laser wavelength. This hampers treatment efficacy in deep-lying lesions. Therefore, to overcome the limitation, we propose a dual thermal therapeutic method in which both laser energy and acoustic energy are simultaneously transmitted for selective treatment of deep-lying tissue. We hypothesized that the rationale for this new method is both thermal addition and increase in the penetration depth of incident light fluence due to the additional acoustic energy. The hypothesis was verified through tissue mimicking phantom experiments. The experimental results demonstrated that the two energies are complementary in elevation of tissue temperature and increase in penetration depth of light fluence, thus resulting in increasing the therapeutic depth by the laser energy. Because of this property, the proposed dual thermal therapeutic method is also beneficial for photodynamic therapy using photosensitizers.