Heat transfer simulation in laser irradiated retinal tissues.

A realistic model of human retinal tissues to simulate thermal performance of optical laser photocoagulation therapy is presented. The key criteria to validate the treatment effectiveness is to ensure the photocoagulation temperature between 60 and 70 °C is reached in the treatment region of interest. The model presented consists of truncated volumes of the retinal pigment epithelium (RPE) and adjacent retinal tissues. Two cases of choroid pigmentation are modelled to signify extreme cases of human eye difference: albino and dark colour choroid pigmentation. Conditions for consistent heating over the irradiated treatment spot is modelled for laser beams with different intensity profiles: 'top-hat', Gaussian and 'donut' modes. The simulation considers both uniform heating within retinal tissue layers and spatial intensity decay due to absorption along the direction of laser propagation. For a 500µm spot, pulse length 100 ms and incident power to the cornea of 200 mW, realistic spatial variation in heating results in peak temperatures increasing within the RPE and shifting towards the choroid in the case of choroidal pigmentation. Finite element analysis methodology, where heat transfer theory governs the temperature evolution throughout tissues peripheral to the irradiated RPE is used to determine the zone of therapeutic benefit. While a TEM01donut mode beam produces lower peak temperatures in the RPE for a given incident laser power, it reduces the volume of retinal tissue reaching excessive temperatures and maximises the zone of therapeutic benefit. Described are simulation limitations, boundary conditions, grid size and mesh growth factor required for realistic simulation.

Effects of Postmastectomy Radiation Therapy on Immediate Tissue Expander and Acellular Dermal Matrix Reconstruction: Results of a Prospective Clinical Trial.

PURPOSE: Postmastectomy radiation therapy (PMRT) delivered to an immediate reconstruction increases the risk of surgical complications. Although acellular dermal matrix (ADM) has been used with immediate tissue expander (TE) reconstruction to improve cosmetic outcomes and minimize capsular contracture, there is a paucity of data on this approach in the setting of PMRT. METHODS AND MATERIALS: Thirty-two patients with stage I to III breast cancer were treated with mastectomy, immediate TE-ADM reconstruction, and PMRT between 2009 and 2012 in a prospective single-arm study. The primary objective was the "success" rate, determined by the number of patients at 2 years after PMRT having an intact final reconstruction, no major complications, and a cosmetic outcome rated by a physician as excellent or good. RESULTS: The median follow-up was 24 months. Final reconstruction status was known in 31 of 32 patients (96.9%; 1 patient left the country) and completed in 29 of 31 patients (93.5%; implant, n = 26; flap, n = 1; both, n = 2; none, n = 2). At 2 years, 6 patients were unevaluable (metastatic disease, n = 3; withdrawn consent, n = 1; left the country, n = 2). Of 26 evaluable patients, the success rate was 65.4% (17 of 26). Lack of success was the result of "fair" cosmesis (n = 2), infection (n = 2), severe capsular contracture (n = 1), major revision (n = 2), and no final reconstruction (n = 2). Most patients had good-to-excellent 2-year overall cosmesis based on patient perception (15; 62.5%) and physician evaluation (19; 79.2%). CONCLUSIONS: To the best of our knowledge, this is the first dedicated prospective trial evaluating long-term cosmetic and complication outcomes in patients treated with immediate TE-ADM reconstruction followed by PMRT. Most patients (65.4%) met the success criteria in this prospective single-arm series. The great majority (93.5%) achieved final reconstruction; most had good-to-excellent overall cosmetic outcomes (79.2%). The results with longer follow-up will be of interest, and further investigation of strategies to optimize reconstruction with PMRT are warranted.