Dose evaluation of nasopharyngeal carcinoma radiotherapy

鼻咽癌放射治療之劑量探討

黃昭源(Chao-Yuan Huang)

指導教授 ： 朱鐵吉

國立清華大學/原子科學院/生醫工程與環境科學系/博士(2009年)

摘要

Radiotherapy is the principle treatment for nasopharyngeal carcinomas. For early stage disease, radiotherapy alone is the treatment of choice. For locally advanced disease, concurrent chemoradiotherapy is recommended and become the standard of care.
Using Monte Carlo simulation and the convolution/superposition algorithm, we examines percent depth dose curves of the central axis in an acrylic phantom with variously sized air cavities for study of longitudinal electron disequilibrium (ED) and for study of lateral ED.
The dose in the rebuild-up region is influenced. The influenced region is on the acrylic phantom surface to a depth of about 0.5 cm. The density scaling method of the convolution/superposition algorithm, applied to heterogeneous media, should be enhanced to account for the overexpansion of the dose kernel in the cavity of ED.
The radiation dose near the interface between high and low atomic number (Z) materials exposed to kilo-voltage photons is enhanced. However, the dose near high-Z interfaces is reduced if the material is thin. Using thermoluminescence dosimeters and Monte Carlo simulation, we found that dose reduction occurs only for gold film thickness less than a micrometer. For kilovoltage photons, the nanometric gold material enhances the nearby dose within 5 mm and this can be used to enhance radiotoxicity in clinic radiotherapy.
It is very important to do every effort for improving the primary local control of nasopharyngeal carcinoma by accurately evaluating the tumor dose and enhancing radiotoxicity in clinic radiotherapy.

關鍵字

鼻咽癌 ； 放射治療 ； 劑量探討

並列摘要

放射治療是治療鼻咽癌最主要的方法，對於初期的鼻咽癌可以選擇只要放射治療就好，對於局部侵犯比較嚴重的病患則會建議同時放射化學治療，而且同時放射化學治療已經成為鼻咽癌的標準療法。
放射治療應用於鼻咽癌治療時，面臨劑量計算上的難題，因為鼻咽腔的空腔會引起電子不平衡現象，導致緊鄰空腔的腫瘤劑量不足，而容易復發。為驗證此假說並建立臨床劑量計算校正參考，運用迴旋疊合演算法與蒙地卡羅模擬法來計算壓克力空腔假體中心軸百分深度劑量曲線。壓克力空腔假體為本研究團隊原創設計，用於研究縱向與側向電子不平衡狀態。
實驗結果顯示：緊鄰空腔的再增建區劑量會受影響，範圍從空腔後壓克力表面到0.5公分的深度。本研究發現，一般臨床常用於鼻咽癌放射治療劑量計算的迴旋疊合演算法，在電子不平衡狀態下的空腔中，計算不均勻介質的劑量，會產生誤差，必須先校正劑量計算的誤差，再治療病患，才能使鼻咽腫瘤接受足夠的劑量而治癒。
當千伏光子經過高原子序與低原子序材料界面時，放射劑量會有加強現象，然而，當材料很薄時，對於高原子序材料界面附近的劑量反而會降低。我們使用熱發光劑量計與蒙地卡羅程式來研究，發現當金膜厚度小於微米尺度時，才會產生劑量降低的現象。但是，當千伏光子照射奈米尺度金膜時，我們的實驗結果發現：小於5 mm 的金膜附近，劑量有加強的現象。將這種劑量加強的效果運用於臨床鼻咽癌病患的治療上，可以增強放射線殺癌細胞的能力。
我們認為，盡一切努力來正確評估腫瘤劑量與增強放射線殺癌細胞的能力，進而提高鼻咽癌病患腫瘤局部控制率是非常重要的。

並列關鍵字

nasopharyngeal carcinoma ； radiotherapy ； dose evaluation

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