電腦放射攝影系統運用於放射治療驗證片可行性評估

The Feasibility Study of Using Computed Radiography in the Verification Imaging of Radiation Therapy

何志偉(Chih-Wei Her) ； 林招膨(Jao-Perng Lin) ； 許世宗(Shi-Zong She) ； 廖漢弘(Han-Hong Liao) ； 施博文(Po-Wen Shih) ； 陳文政(Wen-Cheng Chen)

《放射治療與腫瘤學》 12卷4期 (2005/12) Pp. 285-293

https://doi.org/10.6316/TRO/200512(4)285

摘要

目的：放射治療所採用之治療驗證底片，被廣泛運用於評估接受治療病患之定位準確度及相關配件設定製作之正確性。但儲存空間、管理不易、易遺失及環保等問題也造成些許困擾。鑒於數位化影像為未來發展之趨勢及針對上述情況，本研究試圖以電腦放射攝影系統運用於觀察驗證片效果評估。
材料與方法：決定治療驗證影像品質優良與否的因素，在於影像是否能表現不同密度及厚度之物質的相對對比度。本研究分別以階梯式楔型濾片及人型假體，分別以照射驗證片模式照射驗證底片、電子式照野影像系統與電腦放射攝影系統，並觀察所得影像的變化。
結果：在階梯式楔型濾片影像表現，電腦放射攝影系統在最低條件時即可完全呈現出所有階梯層次。在人型假體影像表現，電腦放射攝影系統在任何部位，其可視灰階表現範圍及不同介質之相對對比度均較治療驗證底片為高。
討論：電腦放射攝影系統由於採用數位技術，動態範圍廣，有較寬的曝光寬容度，即使在一些傳統曝光條件難以掌握的部位如骨盆腔側位也能調整出較好的影像。對放射治療醫師而言，電腦放射攝影系統能清楚區分相對解剖位置，以評估治療計劃給予劑量與實際治療時的符合程度。電腦放射攝影系統，似乎是解決放射治療驗證底片問題之未來趨勢。

關鍵字

電腦放射攝影 ； 治療驗證底片 ； 電子式照野影像系統

並列摘要

Purpose: The conventional verification films and electronic portal images are widely used in the verification of patients' position and the reproducibility of the multi-leaf collimator and block, custom block or cerroben block. The use of verification film is often accompanied by the inconvenience of storing and retrieving. In addition, the importance of using digital images cannot be overemphasized in the modem radiotherapy. We intended to compare digital portal images obtained from computed radiography (CR) system with conventional portal films and the images from electronic portal imaging devices (EPID).
Materials & Methods: The quality of the verification images was based on the contrast of different thickness or density. We took conventional portal films and digital images of a step wedge and an anthropomorphic RANDO Phantom under a 21 EX Varian linear accelerator. Those images were then compared by visual inspection and quantitative analysis method.
Results: Based on the step wedge study, CR system could obtain the full gray-scale of images with least MU. In each treatment site (i.e. Head & Neck, Chest & Pelvis), the quality of the CR images was judged to be superior to conventional portal films.
Conclusion: The operation for the CR system is similar to the tradition verification film. Since they are digital images, they ca be post processed and the anatomic structure can be enhanced in different ways, especially in the lateral fields of pelvis. It provides a better quality of image to verify the accuracy of the treatment position. It seems that the CR system ca provide a better solution for the radiation treatment of cancer.

並列關鍵字

Computed radiography ； Verification film ； EPID