電腦斷層影像金屬假影對於放射
治療計畫系統劑量計算之影響評估

Evaluate Dose Influences Cause by CT Metal Artifact in Treatment Planning System.

郭建宏(Chien-Hung Kuo)

指導教授 ： 田育彰

高雄醫學大學/健康科學院/醫學影像暨放射科學系碩士在職專班/碩士(2020年)

摘要

目的：金屬假影是臨床上常出現的電腦斷層假影，在放射治療計畫系統中對於劑量分佈之計算常與週邊組織真正接受到的輻射劑量有差異。本研究採用輻射變色膠片（Radiochromic film）來量測包埋有高密度金屬物質的假體中的劑量分佈，與治療計畫系統針對同一假體所計算出的劑量分佈做比較；並比較使用不同方式在治療計畫系統中作假影密度覆寫（Override）時，何種方式所得到的劑量分佈結果較為接近實測值。
材料與方法：本研究使用Elekta SynergyTM直線加速器對以石蠟包埋之椎體融合手術金屬植入物進行照射，並採用輻射變色膠片GAFCHROMIC EBT3量測真實劑量，並與治療計畫系統的劑量計算值比較。
結果：以不同假影覆寫方式下，治療計畫系統計算所得之劑量值沒有差異。且在射束被金屬植入物阻擋之前的區域中，劑量量測值及劑量計算值相比的𝒑值為0.24，可說此區域的劑量量測值與劑量計算值沒有差異。而在射束被金屬植入物阻擋衰險之後的區域，劑量量測值及劑量計算值相比較的𝒑值小於0.05，顯示在這個區域中，劑量量測值與治療計畫系統所計算之結果有所差異。
結論：臨床上在治療計畫系統內常使用的假影覆寫方式對於修正劑量計算正確性的效果有限，金屬植入物在電腦斷層模擬攝影影像中被低估的衰減係數對於劑量的計算結果影響更大，在治療計畫的製作上必須予以考慮。

關鍵字

金屬假影 ； 金屬植入物 ； 輻射變色膠片

並列摘要

Purpose: Metal artifact is high-frequency artifacts in clinical CT images. In treatment planning system, this artifact cause inaccuracy in dose calculate for nearby tissue. This study intent to measure the absorb dose beside the metal implant embedded phantom by radiochromic film, then compare with the dose calculate by treatment planning system. And override the density of metal artifact in different method, then compare which method could approach the true dose measure by radiochromic film.
Materials and Methods: This study irradiate the phantom which are metal implant embed in paraffins by Elekta SynergyTM linear accelerator, measure the radiation dose by GAFCHROMIC EBT3 radiochromic film, and compare with the dose calculate by treatment planning system.
Results: There is no difference in two method for override the density of metal artifact. In the area of non-barrier by metal implant, by reason of 
the 𝒑 value = 0.24, also has no dose different between dose calculate by treatment planning system and dose measure by radiochromic film. In the area of attenuated by metal implant, the result in measurement dose and calculated dose are 𝒑 < 0.05, show that is different in treatment planning system with real situation.
Conclusion: The dose accuracy improving by using common method for density override in treatment planning system is very restricted. For treatment planning issue, should more consideration about the under-estimated attention coefficient for metal implant in computed tomography simulation image.

並列關鍵字

Metal artifact ； Metallic implant ； Radiochromic film

參考文獻

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