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錐狀射束電腦斷層影像於可調性放射治療計劃劑量計算之應用發展

The Application of CBCT-Based in the Treatment Planning for Adaptive Radiotherapy

摘要


具備執行影像導引放射治療(Image Guide Radiotherapy, IGRT)功能之直線加速器,其配置之錐狀射束電腦斷層(Cone-beam Computer Tomography, CBCT)主要應用於確保病患接受放射治療時位置的正確性。由於CBCT影像與應用於模擬定位之扇狀射束電腦斷層(Fan-Bean CT, FBCT)影像同樣可呈現出CT值,因此,其具有應用於治療計劃中作爲劑量計算之潛在性。臨床CBCT取得病患接受治療位置之三維電腦斷層影像中,可觀察到癌症病患接受不同分次照射下,腫瘤及身體外部輪廓發生的變化,將造成劑量分佈潛在性誤差,此種誤差難以進行重新擺位而獲得解決。較理想的解決方案爲利用這些臨床上即時取得之CBCT影像,立即重新設計治療計劃。本文藉多位研究者的論文報告,了解並討論以CBCT應用於可調性放射治療(Adaptive radiotherapy),重新進行治療計劃的劑量計算之可行性。結果顯示以CBCT系統取得之影像經過硬體或軟體適當處理修正後,將其應用於治療計劃,產生之劑量誤差將合乎臨床使用所接受之範圍,因此可將CBCT運用於可調性放射治療計劃的劑量計算上。此一結果應用於身體各部器官治療時,須注意在生理運動造成的動態假影與被照體較大產生較多散射等影像劣化因素,爲CBCT應用於治療計劃所面臨之最大限制,故以頭頸部癌症患者執行可調性放射治療作相關評估。

並列摘要


Image-guided radiotherapy (IGRT) was carried out on a medical linear accelerator with cone-beam CT (CBCT) to assure the geometric accuracy of patient setup. Potentially, the CBCT image data was provided with CT number like Fan-Bean CT (FBCT) can also be used for dose calculation m the treatment planning of radiotherapy. In the clinical practice of IORT, changes in tumor size and contours during the course of radiotherapy can be observed in CBCT images at different fractionations. The discrepancy of dose distribution resulting from these changes can not be corrected by simply repositioning the patient. One ideal strategy is real-time replanning based on acquired CBCT images. This study reviews several previous publications on the application of CBCT-based replanning in the adaptive radiotherapy, and evaluates its dosimetric feasibility. The results of these studies lead to the conclusion that CBCT-based dose calculation achieved a clinically acceptable prescription, and can be used in adaptive radiotherapy with appropriate apparatuses and/or computer programs to modify CBCT images. However, it should be used cautiously especially when the image quality could be deteriorated by factors such as larger extent of organ motion or greater amount of scatter resulting from large field sizes, which pose the greatest limitation on CBCT-based dose calculation. Therefore, it seems most feasible to apply CBCT-based dose calculation to the adaptive radiotherapy of head and neck malignamcies.

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