前言:本研究之目的,為在臺北榮民總醫院發展利用直線加速器給顱內小腫瘤單次高劑量之照射方法。其照射精準度在機械幾何上可達1 mm,而在劑量之準確度可達3%之誤差範圍內。材料與方法:本研究設備是採用Varian CL-1800直線加速器與Leksell立體定位系統。治療技術則使用多量非共面弧形照射並配合附加於鉛擋板溝槽之二級準直儀,其內部之圓柱形準直器之材質為10 cm厚之不?袗?,其照野直徑由15 mm到30 mm,可準確的限制劑量僅落於照射點上,而對於照射區之外,則劑量將會急速的向外下降;病患固定系統則包含立體定位固定環與固定於治療床的立體定位底座;定位框及等中心點指示器則用於定出照射靶擊中心位置;深度量尺可用來測量腫瘤距各不同方向與截面之照射深度。結果:此系統測試之標準須達到1 mm之機械幾何之準確度,在劑量之準確度須達到3%;準直系統之漏射量須小於7%。劑量輸出率及組織與假體比表格已建立可供計算劑量，等劑量分佈圖也已利用水假體測試系統建立完成，並經LiF熱發光晶片驗證。討論:三度空間頸部立體定位放射治療計畫系統在整個計畫中扮演著一個不可或缺的角色。而可用於測量至5 mm直徑大小照野面積之偵測器以及精密度達到1 mm以下的光密儀,亦為從事放射手術品質管制中必備的儀器。結論:本研究之設備與基礎劑量研究都已完成,此技術已可供日後臨床使用與評估。

　　　　　 Purpose: The aim of this study is to develop a technique at Veterans GeneralHospital-Taipei to irradiate small lesion in the brain to a high dose per fractionwith 1mm geometric accuracy and 3% dosimetric accuracy. Materials and Methods: Thetechnique employs Varian CL-1800 linear accelerator with 10 MV X-Ray and the Leksellstereotactic system. This treatment technique combines with multiple non-coplanararc irradiation and secondary rigid collimator mounting to the slot of block tray.The cylindrical collimator inserts are made by stainless steel with 10 cm thickness.Their field size opening range from 15mm to 30mm in diameter and confine the accuratedose to the target and steep dose fall-off outside the target volume. The patientfixation system consists of stereotactic base ring and head fixing posts that canbe directly mounted on the treatment couch. The target position frame and isocenterfront pointer are used for adjusting the target point of isocenter. A ruler is usedfor measuring depth of tumor at various planes and directions.Results: This system was systematically tested within 1-mm mechanical geometric and2% dosimetric accuracy respectively. All of collimator inserts showed no flaw andthe radiation leakage was less than 7%. Dose rate and tissue-phantom-ratio table hadbeen setup for dosimetry purpose. Isodose curve were established by water phantomand verified by radiation sensitive films and TLD dosimetry.Discussion: A three-dimensional computerized treatment planning system is essentialfor stereotactic radio-surgery device. Dosimetry detetors capable of measuring 5-mmdiameter field and film dosimetry with 1mm accuracy are indispensable equipment forquality control of this radiosurgery procedure.Conclusion: Apparatus test and basic dosimetry study had been complied. The techniqueis ready for future pre-clinical study and evaluation.