目的:為瞭解多功能西門子PRIMUS 3008直線加速器之虛擬式楔型濾器在臨床應用上之物理特性，針對虛擬式楔型濾器的角度、穿透因子，及其與實體式楔型濾器的相對劑量分布曲線做一比較分析，以作為在臨床治療計畫系統使用上能有效的執行。材料與方法:使用IC 15游離腔在Wellhofer 48×48×40cm3的水假體中，在SSD 90公分，距中心軸水面下10公分處，測量虛擬式楔型濾器角度;在中心軸水面下5公分(6 MV)和10公分(15 MV)處測量穿透因子，SSD為100公分。另外使用Wellhofer CA24陣列式游離腔，在不同的深度(6 MV時深度分別為dmax、5、15、20公分;15 MV時為dmax、10、15、20公分)和不同的濾器角度(15、30、45、60度)下，量測虛擬式和實體式楔型濾器的相對劑量曲線分布圖。結果:虛擬式楔型濾器角度在機器設定值與實際量測計算所得之間的誤差在1.5度範圍內，而穿透因子趨近於定值(約為1)。由虛擬式楔型濾器和實體式楔型濾器在不同深度、角度時的相對劑量分布曲線變化，發現虛擬式楔型濾器所形成的劑量曲線分布並非完全與實體式楔型濾器相同。結論:虛擬式楔型濾器擁有比實體式楔型濾器更靈活的應用,但必須對於治療機的物理特性有充分的瞭解，關於治療機的品質驗證更是一大重點，如劑量率的變化、連續性的角度變化，如此才能真正的確保並提高治療品質。

　　　　　Purpose: The purposes of this paper are to analyze the clinical physical characteristics ofvirtual wedges for the Siemens PRIMUS 3008 linear accelerator. We focus on the wedge angles,transmission factors and the discrepancies of relative dose distributions between physical andvirtual wedges. The data will be used to set up the computer treatment planning database.Materials and Methods: We measure virtual wedge angles and transmission factors by Wellhofer IC15, 0.13 cc chamber. The wedge angles are measured at 10 cm depth of the central axis, and SSD is90 cm. Transmission factors are measured at 5 cm (6 MV) and 10 cm (15 MV) depth of central axis,and SSD is 100 cm. The relative dose profiles of virtual and physical wedges are measured byWellhofer CA24 chamber array. We measure four depths of the central axis (the depth are dmax, 5,15, 20 cm for 6 MV, and dmax, 10, 15, 20 cm for 15 MV) for four wedge angles. The chamber isinstalled on the chamber frame of Wellhofer water phantom (48×48×40 cm3).Results: The different range of virtual wedge angles is below 1.5 degrees between the machinesetup and the results measured by ion chamber. The transmission factors of virtual wedges remainalmost constant. The relative dose profiles of virtual and physical wedges were not completely thesame.Conclusion: The clinical applications of virtual wedge have convenience for treatment setup, andvarious arbitrary angle. In order to promote the quality of treatment, the QA program becomes veryimportant.