- 學位論文
輻射防護劑量計算之研究：劑量轉換因數、診斷和治療有效劑量評估
Computational Study of Radiological Protection Dose: Dose Conversion Factor, Diagnostic and Therapeutic Effective Dose Evaluation
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摘要
輻射防護劑量為評估輻射曝露風險的重要參考基準。國際放射防護委員會所定義之輻射防護量，一直是世界各國訂定相關游離輻射防護法律、規範、指引的依據。經過多年的發展，國際放射防護委員會已針對輻射曝露風險建立一套完整的評估系統。由於不論是器官劑量、或是全身劑量的評估，輻射防護量均定義在人體上，無法以實驗測量方式獲得。因此必須以程式配合數值假體進行模擬計算，方能求得輻射防護量。 本研究利用數學假體及體素假體兩種性質不同的數值假體，藉由蒙地卡羅計算機程式針對國際放射防護委員會所定義的輻射防護量進行研究。對於體外照射對不同年齡層假體造成之劑量轉換因數的影響、放射診斷最常使用的X光照相檢驗之曝露風險評估、以及硼中子捕獲治療造成的輻射防護量，均做詳細的模擬計算及討論。經研究發現，劑量轉換因數與年齡有一定依存關係，現今僅使用成年人劑量轉換因數進行屏蔽計算，對某些場合或應用可能會有低估的疑慮。輻射防護量在X光放射診斷的應用亦於本研究中探討。計算後發現，不同的X光管電壓與不同的照射方式對輻射防護量有明顯的影響，不論是胸部或腹部X光照相檢驗，有效劑量均與峰值管電壓成正比。另外，依據不同射源項特性、不同照射幾何、不同數值假體、不同防護量建議，硼中子捕獲治療造成之等價劑量與有效劑量亦經過詳細的分析與討論，計算結果發現照射幾何對有效劑量評估結果有明顯的影響，尤其是採用ICRP 103號報告之建議時。本研究之成果，期能提供國內硼中子捕獲治療研究與發展之參考。
並列摘要
Protection quantities are important tools for the assessment of stochestic effects induced by radiations. Nowadays the concepts brought up by ICRP are well developed and are widely adopted in the laws, regulations and guidences. Since the protection quantities are defined in a human body, it is very difficult to measure those quantities directly. Therefore the only way to acquire the equivalent dose and the effective dose is through simulations. In this study, the equivalent dose and the effective dose were evaluated by a Monte Carlo code, MCNP, and by the numerical phantoms. Both a methematical phantom developed by Eckerman and a voxel phantom of ICRP Publication 110 were used in the calculation. Age-dependent protection quantities for external irradiations, the equivalent dose and effective dose results from the X-ray diagnosis and from the boron neutron capture therapy were evaluated and discussed in detail. The dependence between the age and the protection quantities shows that using only the dose conversion factors for adults may result in underestimations. For the X –ray radiological diagnosis, the peak tube voltage of the X-ray tube and the irradiation geometry severely affect the protection quanties evaluated. Especially for the radiological therapy, the treatment planning not only needs to focus on the dose in the tumor, but also take the exposure risk of the normal tissue into account. The parameters of the boron neutron capture therapy, such as source terms, irradiation geometries, phantoms, recommendations on radiation quantities, were all considered in the calculations. Their impact were also discussed.
參考文獻
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