Numerical optimization of laser radius ratio and power in photothermal therapy of various ellipsoidal tumor shape.

Cancer remains a major global health burden, and the incidence of skin cancer has steadily increased over the past several decades. Among various treatment modalities, photothermal therapy (PTT), a noninvasive technique, has attracted considerable attention due to its advantages of minimal bleeding and rapid recovery. Although extensive research on PTT has been conducted, most numerical studies have simplified tumors into cylindrical or spherical geometries, which fail to adequately represent the geometric irregularities of real tumors. To overcome this limitation, tumors were modeled as ellipsoids with varying aspect ratios, and a numerical analysis was performed by integrating Monte Carlo simulations with heat transfer calculations. Specifically, a systematic parametric study was conducted using the tumor aspect ratio, laser beam radius ratio, and irradiation power as variables to quantitatively evaluate the photothermal therapeutic efficacy. By employing the Arrhenius thermal damage model to analyze the laser power required for tumor ablation, it was revealed that the required power exhibits a U-shaped behavior with respect to the radius ratio. Additionally, it was confirmed that although thermal damage to normal tissue progressively decreases as the laser radius ratio increases, applying an excessively large radius ratio requires very high laser power, and is thus accompanied by clear physical and clinical constraints. Ultimately, by comprehensively considering the spatial energy distribution of the Gaussian beam and the geometric complexity of the elliptical tumor, these findings suggest that the conventional approach of simply matching the beam radius to the tumor radius must be reconsidered.