A simulation-based optical safety framework for dermatologic laser wavelength selection across Fitzpatrick skin phototypes

Abstract

Abstract Laser wavelength selection in dermatology remains challenging across diverse skin phototypes, where inappropriate choice may increase the risk of epidermal injury. This study develops a simulation-based optical safety framework to support wavelength selection by quantifying phototype-dependent epidermal energy deposition and dermal-to-epidermal energy balance. A Monte Carlo light-transport model was used to simulate photon propagation in a three-layer skin model across Fitzpatrick skin types I–VI. Four commonly used dermatologic wavelengths (532, 755, 808 and 1064 nm) were evaluated. Epidermal energy deposition was quantified using the Epidermal Thermal Risk Index (ETRI), and dermal-to-epidermal energy balance was quantified using the Benefit–Risk Ratio (BRR). ETRI categories were defined as heuristic interpretive ranges. A composite score combining safety and energy-balance components was computed and tested across multiple weighting schemes via sensitivity analysis. Shorter wavelengths produced markedly higher epidermal energy deposition, particularly in higher phototypes. At 532 nm, ETRI rose monotonically with melanin content, indicating elevated epidermal optical burden. In contrast, 1064 nm maintained the lowest ETRI values across all phototypes. Across five tested weighting schemes, including extreme configurations, 1064 nm consistently demonstrated the highest composite score in every phototype (Spearman ρ = 1.00 against the equal-weight baseline), supporting robustness of the framework. This study presents a simulation-based optical safety framework that translates wavelength-dependent energy deposition into an interpretable structure for laser wavelength selection. Within the assumptions of the model, longer wavelengths — and 1064 nm in particular — demonstrate the most favorable epidermal safety profile and dermal-to-epidermal energy balance across higher phototypes. The framework is intended as relative optical safety guidance and must be integrated with treatment indication, target chromophore, fluence, pulse duration, epidermal cooling, device-specific settings and operator experience in clinical practice.