Evaluation of photothermal therapy effectiveness based on real-time laser radius modulation guided by diffusion behavior analysis

• Diffusion-based laser radius modulation improves photothermal therapy selectivity. • A physics-based correlation links nanoparticle diffusion to laser radius setting. • Treatment efficiency increases by balancing tumor damage and normal tissue injury. • An effective Arrhenius metric quantifies tumor and normal tissue damage balance. Cancer can arise in diverse anatomical sites, requiring treatment strategies tailored to tumor location. However, conventional therapeutic modalities are often associated with inherent limitations and side effects, motivating the development of alternative approaches. Photothermal therapy has gained attention as a noninvasive treatment that achieves localized heating through photothermal conversion. In this study, the therapeutic performance of photothermal therapy for skin cancer was investigated using numerical analysis. Gold nanoparticles with different aspect ratios were employed as photothermal agents, and their time-dependent spatial distribution following intratumoral injection was analyzed based on diffusion modeling. On the basis of the calculated nanoparticle distribution, a diffusion-guided strategy was implemented in which the laser irradiation radius was dynamically modulated to selectively target nanoparticle-enriched regions. Numerical simulations were performed by varying the nanoparticle aspect ratio, treatment starting time after injection, and laser power. The resulting temperature distributions were used to compute the Arrhenius thermal damage ratio and the effective Arrhenius thermal damage ratio, enabling quantitative evaluation of therapeutic outcomes. For each nanoparticle aspect ratio, the optimal treatment starting time and laser power were identified. Importantly, diffusion-guided laser radius modulation enabled more selective heating of nanoparticle-enriched tumor regions. Compared with fixed-radius irradiation, dynamic radius adjustment increased the maximum achievable therapeutic performance by up to 13%. Clinically, this enhanced spatial selectivity may improve treatment safety and support more precise, patient-specific photothermal therapy planning. Overall, the proposed approach enhances control over thermal dose delivery and has the potential to improve both the efficacy and safety of photothermal therapy.