電腦斷層攝影應用於放射治療計畫之商榷

Discussions on the Implication of Computed Tomography for Radiation Therapy Treatment Planning

賴耿光(K. G. Lai) ； 梁棉榮(M. W. Leung) ； 李玉麟(Y. L. Lee) ； 陳光耀(K. Y. Chen)

《中華放射線醫學雜誌》 9卷3期 (1984/09) Pp. 212-220

摘要

電腦斷層攝影對於腫瘤的治療可提供兩種用途：(1)測定腫瘤的範圍並追踪其對治療的反應，(2)告訴吾人有關腫瘤的位置、大小、病人的體形輪廓與組織組成等，以上因素皆會影響到體內的劑量分布。電腦斷層攝影所產生的CT讀數（與診斷X射線的線性衰減係數有關）可以反映相關組織的電子密度。由CT讀數所組成的排列經轉換成物理密度，然後對組織之不等密度加以修正，再代入個別治療條件，所求得之等劑量曲線經描繪並顯示在治療計劃的電腦上。到目前為止，這種運算過程所需之軟體尚未應用到本院常規電腦化治療計畫上，價錢其中是一個考慮的因素。另外一種應用電腦斷層影像於治療計畫之較簡單方法即將影像放大至實際尺寸並由此描出病人體形輪廓，不等密度之組織以及腫瘤體積。在指出各不同區域之適當電子密度值以後，這些數據即輸入目前的治療計畫系統。本文之目的乃在探討電腦斷層攝影應用於放射治療計畫之潛在價值及可能遭遇的問題，其適用性與準確性，並舉一些臨床實例加以說明。

並列摘要

Computed tomography (CT) provides advantages in tumor management in two ways: (1) Demonstrate the extent of the tumor and show their response to the treatment, and (2) provide information about tumor location, size, patient contours and tissue composition etc., these factors affect the dose distribution within the tumor and the body.
The basic yields of a CT scan, the CT numbers, are related to the attenuation coefficient of the diagnostic X-rays, actually reflect the electron densities of the individual tissue concerned. The array of CT numbers may be convered back to tissue densities and is then used to do a complicated correction for tissue inhomogeneities. The isodose curve thus calculated may be plotted and demonstrated on a treatment planning system. So far, the soft ware required for this calculating procedure is still not available to the routine treatment planning of our Varian R07 computer system. A simplier utilization of CT scan to the computerized treatment planning is to enlarge the CT image to the life size and then input the patient contour, heterogeneities and tumor volume into the treatment planning program. After assigning the appropriate density values to the various regions, tissue correction can be calculated for isodose curves construction. The purpose of this study was to investigate the potential advantages of computed tomography used in the radiation treatment planning and the possible problems encountered, the applicability and the accuracy etc. Several clinical examples will be demonstrated.