Ultrasound-Assisted Photothermal Therapy (ULTRA-PTT) for the Treatment of Deep-Seated Tumors

Photothermal therapy (PTT) has garnered considerable attention as an attractive treatment tool for cancer due to precisely selective treatment and minimal side effects. The primary challenge of PTT, which hinders its widespread application, is the limited therapeutic depth. This limitation arises from optical scattering in biological tissues, causing inadequate heat distribution within the deep tissue. To overcome this challenge, ultrasound-assisted PTT (ULTRA-PTT) is proposed that leverages the temporary formation of gas bubbles induced by ultrasound within the light propagation path. These bubbles act as optical clearing agents, effectively reducing optical scattering in biological tissues. To facilitate ULTRA-PTT, a dedicated handpiece consisting of a ring-shaped ultrasound transducer and a laser delivery module is developed. In-vivo experiments show that ULTRA-PTT statistically outperforms conventional PTT in melanoma treatment, mostly due to its ability to deliver sufficient laser energy to deep-seated cancer cells. These findings underscore the potential of ULTRA-PTT to expand the clinical applications of PTT beyond local tumors occurring in superficial tissue.