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Hardware acceleration of a Monte Carlo simulation for PDT treatment planning

Monte Carlo (MC) simulations are being used extensively in the biophysics, particularly for modeling light propagation in tissues. The high computation time for MC limits its use to solving only the forward solutions for a given source geometry, emission profile, and optical interaction coefficients of the tissue. However, Photodynamic Therapy (PDT) treatment planning requires solving the inverse solution of a desired dose distribution. A faster means for performing Monte Carlo simulations would enable the use of MC-based models for solving the inverse problem. To explore this possibility within the context of PDT treatment planning, a digital hardware implementation of a Monte Carlo simulation based on the Monte Carlo for Multi-Layered media (MCML) software is presented. This hardware design, implemented on a development platform with multiple Field-Programmable Gate Arrays (FPGAs), performed the Monte Carlo simulation approximately 80 times faster than the MCML software running on a 3GHz Intel Xeon processor. It is projected that the hardware design, called FPGA-based MCML (FBM), can run up to 280 times faster than MCML if using the most recent FPGA technology. The isofluence lines generated by FBM differ from those generated by MCML by only 0.1-0.2 mm. 4 1 Introduction Photodynamic Therapy (PDT) is an emerging treatment modality in oncology and other fields. Improvements in PDT efficacy, particularly for interstitial applications, require faster computational tools to enable efficient treatment planning. The fundamental mechanism of PDT is the systemic administration of a photosensitizer, followed by the irradiation of the target volume with light of a specific wavelength to activate the photosensitizer. 1-4 Advances in PDT have allowed this therapy to be applied to more complicated treatment volumes, particularly in interstitial applications such as those in the prostate and the head and neck region. 5-9 Compared to conventional treatments such as surgery, radiotherapy, and chemotherapy, PDT is a minimally invasive procedure that achieves tumor destruction without systemic toxicity. This is especially beneficial for head and neck cancers, since the surgical resection of even small tumors can lead to functional impairment or disfiguration. 10 In order to maximize the efficacy while reducing complication rates, it is important to employ accurate models of light propagation in turbid media that can take into account complex tumor geometry and the heterogeneity in the tissue's light interaction coefficient and responsivity to PDT, for clinically robust treatment planning. Among other factors, light dosimetry plays a critical role in PDT treatment planning. Selective tumor …