Scatter‐limited phototherapy: A model for laser treatment of skin

Background and Objectives To effectively deliver laser light into the skin for non‐ablative resurfacing, hair removal, and other applications, one must account for scatter, absorption, and thermal diffusion. A novel method to control the penetration of laser light into tissue is proposed. This method uses the incident beam diameter, the pulse duration, and the intrinsic light scattering of tissues such as skin to limit the laser light penetration and thermal damage. We term this innovative laser delivery concept ‘scatter‐limited phototherapy’. Study Design/Materials and Methods This study demonstrates how the delivery mechanism simplifies the non‐ablative treatment of sun‐damaged skin. Calculations are based upon Gaussian scatter of light and isotropic thermal diffusion. Calculations of light distribution and profiles of temperature increase are created. Results Using an optical fiber delivery system with the appropriate diameter, coupled with skin surface protection, one can create thermal damage at a given depth with preservation of the epidermis. Conclusions Scatter‐limited phototherapy is a predictive model, allowing one to design better laser delivery systems. Scatter‐limited phototherapy should also be applicable to other fields of dermatologic surgery, such as hair removal and the treatment of vascular lesions. Additionally, other medical specialties will be able to use the concept of scatter‐limited phototherapy to predict and better understand laser–tissue interactions. Lasers Surg. Med. 30:381–388, 2002. © 2002 Wiley‐Liss, Inc.