評估鈷化生物玻璃標誌物對放射治療劑量擾動的影響

目的: 目前臨床所使用的標準Fiducial marker的材質多含有高原子序金屬物質，例如：金。此類物質在進行CT simulation時會有嚴重的金屬假影發生，導致治療計畫製作時會有劑量擾動的情況。本次研究將比較生物玻璃(Bioglass, BG)、鈷化生物玻璃(CoBG)以及標準臨床用的Fiducial marker對劑量擾動造成的影響。材料與方法: 我們透過電腦斷層掃描取得純假體影像以及含有兩種不同方向的Fiducial marker假體影像。光子治療的部分透過Pinnacle治療計畫系統去比較不同種類的Fiducial marker對整體劑量以及劑量分布的差異。質子治療則是使用蒙地卡羅模擬的方式模擬窄射束穿過以及未穿過Fiducial marker後的劑量擾動。同時為了解電腦斷層影像重建中的金屬假影消去法(Metal Artifact Reduction, MAR)對劑量擾動的影響，以上兩種治療的實驗皆有比較FBP(Filtered Back Projection)以及MAR的重建方法。結果: 研究顯示使用Fiducial marker去進行影像導引式的放射治療在整體腫瘤劑量分布上會根據Fiducial marker的原子序、大小以及相對於射束的方向，得到不同程度的劑量擾動。結論: 我們自製的在光子治療以及質子治療的實驗中與市售的Fiducial marker觀察到的劑量擾動差異與市售的Fiducial marker差不多，而其金屬假影的干擾情況則是優於其餘五種市售Fiducial marker。CoBG以及BG不會產生嚴重金屬假影因此在劑量上可以不用擔心因為MAR重建後產生的不正確性，也可以避免MAR引起幾何變形的問題。

PurposeFiducial markers which use in clinical are usually made by material with high atomic number (ex: gold). This kind of material will cause serious metal artifact while doing CT simulation, and will also cause dose perturbation. Our research want to realize the dose perturbation of Bioglass (BG), Cobalt-bioglass (CoBG) and other five fiducial markers. Materials and MethodsWe acquire CT images of phantom and phantom with two orientation of fiducial marker. In photon, we use Pinnacle treatment planning system to see the dose perturbation and distribution. In proton, we use Monte-Carlo to simulate the difference between fiducial markers. We also compare metal artifact reduction (MAR) with filtered back projection (FBP) to see the perturbation difference.Result The perturbation of fiducial marker that use in image-guided radiation therapy (IGRT) will appear some difference, according to the atomic number, size, orientation of fiducial marker.ConclusionIn dose perturbation, our fiducial markers are similar to the fiducial markers that use in clinical. In artifact, our fiducial marker are better than those use in clinical. CoBG and BG fiducial marker can let alone the perturbation that affect by algorithm, in the reason that they didn’t cause metal artifact.