雷射間質熱療（Laser Interstitial Thermal Therapy, LITT）是一種利用雷射光束產生熱量破壞異常組織，進行局部腫瘤燒灼之微創治療技術，臨床上常與核磁共振造影（magnetic resonance imaging, MRI）結合，以輔助雷射探針定位及周圍溫度監控，其治療範圍受雷射參數、組織光學性質與冷卻效率影響。建立準確且高效率之數值模擬模型，以預測治療過程中的溫度分布與壞死區域，已成為提升 LITT 安全性與治療規劃的重要研究方向。本研究旨在建構一套適用於 LITT 的數值模擬模型，以預測治療過程中的熱分布行為。
本研究採用計算流體力學（computational fluid dynamics, CFD）進行數值計算。在熱源架設方面，使用 3D 球型光源近似雷射探針之加熱效果，並搭配生物熱傳方程式模擬人體組織血液之散熱。同時依據人體組織之吸收係數（absorption coefficient）計算局部雷射能量吸收，並考慮光線通過不同介質時的吸收遞減效應，以降低傳統幾何光學模組之計算成本，建立完整之 LITT 熱傳數值模型。研究中先以參考文獻之基準探針（探針 B）進行設計與比較，驗證本模型於溫度場與損傷分數分布上具有相似趨勢；再將此方法應用於開發中之探針 I，分析不同雷射功率、冷卻流量與冷卻流體對治療範圍之影響。
結果顯示，雷射功率為影響損傷範圍與壞死區域大小之主要因素；當探針 B 功率由12W降至9W時，損傷面積降低 32.7%。提高冷卻流量可降低探針周圍熱累積，使損傷與壞死範圍縮小；當探針B冷卻流量由2.5×10-6 m3/s增加到7.5×10-6 m3/s時，損傷面積降低約10.6%。探針I更換冷卻流體後，熱量可更有效沉積於探針周圍組織，形成較明顯之損傷與壞死區域。整體而言，本研究建立之等效熱源模型可用於預測 LITT 溫度場與熱損傷分布，並作為後續治療參數設計與探針冷卻系統開發之參考。

Laser interstitial thermal therapy (LITT) is a minimally invasive thermal-ablation technique in which laser energy is delivered through an optical-fiber catheter to destroy pathological tissue while magnetic-resonance thermometry is used to monitor treatment. Because the final ablation region depends on laser power, heating duration, tissue properties, blood perfusion, catheter geometry, and coolant performance, an efficient numerical model is required for treatment planning and probe development. This study establishes a three-dimensional computational-fluid-dynamics (CFD) model that represents the diffuser tip by five equally spaced spherical heat sources. Irradiance decreases through geometric spreading with exponential attenuation across the optical fiber, coolant, catheter shell, and tissue, and the resulting volumetric heat source is coupled with transient heat transfer, coolant flow, and the Pennes bioheat equation.
Two catheter designs are investigated. Catheter B is a published baseline design using carbon-dioxide cooling, whereas catheter I is a preliminary design developed with the Industrial Technology Research Institute and initially uses water cooling. Grid, time-step, and source-number tests indicate that approximately three million cells, a 0.1 s time step, and five sources provide stable results. For catheter B at 12W and 240 s, the predicted maximum temperature is approximately 65℃, compared with about 68℃ in the reference calculation. Redistributing 3-5% of the laser power to the sapphire shell as an approximate scattering correction increases the maximum temperature to 67.8-69℃ and produces a more rounded temperature field. Threshold-time, CEM43, and Arrhenius damage measures are compared, and the threshold-time indicator is retained for geometric parameter analysis.
Parametric calculations are performed for laser powers of 9-12W and five coolant flow rates. Laser power is the dominant factor governing the overall damage and necrotic regions, while increasing coolant flow mainly suppresses local heat accumulation near the inlet and posterior probe region. In catheter B, increasing the mean CO2 speed at 12W reduces the maximum temperature, damage area, and necrotic area. Water-cooled catheter I forms a more complete elliptical damage field, but its maximum temperature may occur inside or near the water-filled probe and therefore does not always indicate tissue necrosis. Replacing water with CO2 shifts the hottest region toward the surrounding tissue and produces a clearer necrotic zone. The proposed equivalent-source model efficiently captures the principal thermofluid trends and can support treatment-parameter selection and cooling-system development; experimental calibration of absorption, scattering, perfusion, and temperature-dependent tissue properties remains necessary.

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