電子射線應用長照射筒之劑量學特性

當治療口腔、陰道腔等小範圍腫瘤、選擇用腔內照射筒是一個很好的治療方式，經設計做成平孔及斜孔為1.8 cm、2.5 cm及3.0 cm不同直徑延伸照射筒，接在Varian直線加速器(Clinic-18)電子射線10×10標準照射施用器上使用。用劑量分佈自動分析系統、水假體及空氣游離腔測量(上標 6,9,12,15,18MeV)不同能量電子射線特性及劑量分佈，校正測量數據有實用範圍、中心軸百分深度劑量、制動輻射、照野平坦性、等劑量曲線及照射筒外圍劑量的百分比。結果顯示不同能量時其Rp、dmax、d80等與原廠製造標準照射施用器的射特性明顯改變。不同的能量最大劑量深度範圍變寬，射束均一性顯示在照射筒內沿為中心劑量的80%、外沿0.2 cm即降為10%以下，X射線污染6%以內，距照射筒外緣0.5 cm接受的劑量在5%以內，照野面平坦性、對稱性及均一程度等分佈與標準照射筒相近，但均優於低能量淺部治療X射線，可以有效、方便的應用於臨床治療。

關鍵字

百分深度劑量；制動輻射；照野平坦度；等劑量曲線圖

並列摘要

The availability of extension cones for electron beams provides more flexibility and treatment approaches to small or intracavitary lesions, such as oral, vaginal or uterine cervical tumors with better homogeneity and depth dose than in the case of superficial x-rays. Circular extension cones of diameter 1.8-3.0cm were fabricated and adapted to the electron applicator of linear accelerator. Dosimetry of the radiation field under the cones and around the walls of the cones were investigated in water phantom, including electron beam energy, practical range (Rp), central axis depth dose and Bremsstrahlung components, field flatness, isodose curves and dose distribution around the outside of cone walls . The extension cones were made of stainless steel and the thick. ness of the walls is 2mm. The dose at outside surface of the cone wall is less than 10%, and dose at 0.5cm from the surface is less than 5%, of the dose dmax in the cone field. Comparison of the cone dosimetry with that of standard applicator showed that the effective depth of the cone is lesser and dmax is closer to the surface. X-ray contamination is slightly higher, approximately 6%. Beam flatness and homogeneity of the cone is similar to the standard applicator.

並列關鍵字

percentage depth dose ； bremsstrahlung ； field flatness ； isodose curve

國際替代計量

電子射線應用長照射筒之劑量學特性

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