- 期刊
直線加速器虛擬式楔型濾器之量測—濾器角度與剖面劑量分佈
The Measurement of Virtual Wedge for Siemens Primus Linear Accelerator-Wedge Angle & Beam Profile
摘要
目的：SIEMENS Primus直線加速器的虛擬式楔型濾器，是照射期間利用監控單位劑量率的變化與準直儀擋塊的移動，來模擬固定式楔型濾器的剖面劑量分佈曲線。本文主要是針對濾器期望角度與剖面劑量分佈曲線兩部份，來比較虛擬式楔型濾器與固定式楔型濾器之問的差異性，並評估虛擬式楔型濾器在臨床應用之可行性。 材料與方法：本文使用Memorial 1.0c.c平行板式遊離腔、量測每一監控單位對劑量之校正比例(MU/dose)，以驗証虛擬式楔型濾器對臨床應用的劑量設定；使用WELLHOFER WP700水假體系統，量測虛擬式楔型濾器的期望角度；並以Sun Nuclear The Profiler陣列式固態偵檢系統量測虛擬式楔型濾器，與固定式楔型濾器的剖面劑量分佈曲線。 結果：對於固定式楔型濾器常用的四種角度15°、30°、45°及60°而言，6MV及18MV的虛擬式楔型濾器相對期望角度的偏差值均在±1.5°以內；剖面劑量分佈部份，6MV的虛擬式楔型濾器與固定式楔型濾器最大偏差值為：濾器角度60°，深度5cm處照野15×15 cm^2為5.0%；而18MV在深度超過5cm後，濾器角度60°，深度10cm處照野20×20cm^2為5.7%，但18MV深度若未起過5cm則最大偏差值會達到11.1%。 結論：基於此一設備不同於以往的觀念及治療方式，因此在臨床放射治療之前須有完整的驗證報告及完善的測試措施，並配合定期的品質驗證工作以確保醫療之品質。
並列摘要
Purpose: The virtual wedge which is equipped in Primus uses dose rate variation and collimator jaw motion to simulate the isodose distribution of hard wedge. The purpose of this report are to compare the differences between virtual wedge and hard wedge for desired wedge angles and beam profiles, and to evaluate the feasibility of virtual wedge clinical application. Materials and Methods: The Memorial 1.0 c.c. parallel plate chamber was used to measure the ratio of MU/dose, to verify the clinic dosimetry sets of virtual wedge. The WELLHOFER WP700 water phantom system with ion chamber was applied to measure the desired angle (α.) of VW. The beam profile data was measured by the Sun Nuclear The Profiler linear array of solid-state detectors. Results: Compared with the 4 commonly-used wedge angles, namely, 15°, 30°, 45° and 60°, the deviation of desired virtual wedge angle for 6 MV and 18 MV photon beam are all within one-and-half degree. For beam profiles, the maximum deviation between VW and HW for 6 MV was 5.0% with wedge angle of 60°, depth of 5cm, and field size of 15×15cm^2. For depth beyond 5cm the maximum deviation between virtual wedge and hard wedge for 18 MV was 5.7% with wedge angle of 60°, depth of 10cm, and field size of 20×20cm^2. However, for depth less than 5cm, the maximum deviation for 18 MV will be as high as 11.1%. Conclusions: Due to the different concept and the clinical application of virtual wedge, we need a comprehensive verification data before we apply the virtual wedge technique in the clinics. We also need to set up and practice a quality assurance program for virtual wedge system to assure the treatment quality.
延伸閱讀
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