呼吸運動導致治療劑量的不確定性，要精確掌握呼吸時之身體解剖位置變化才能正確評估治療成效。4DCT技術可提供呼吸時完整之人體解剖訊息，使用傳統螺旋式CT來獲取4DCT影像以分析其影像體積特性是本研究之目的。我們設計呼吸移動模擬假體來模擬簡單的一維呼吸運動，系統包含馬達齒輪傳動系統及三個不同大小及密度的球型假體。設定好運動週期及運動長度之假體使用Spiral CT掃描後，依據掃描條件對影像做相位篩選及重組，可以獲得4D之影像。不同相位之影像組被傳入治療計畫系統後，以自動輪廓繪製功能用不同之閾值HU(-200, -500, -700)畫出假體球之輪廓，觀察其形狀並計算其體積。結果：不同相位影像組隻評俊體積與景泰影像體積之比值從0.83至1.39、體積小之假體體積變化比大體積假體大、密度高之假體所組出來之體積較大、運動週期較短時體積變化較顯著。未分相位之影像所組出來肢體形狀會因開始掃描之相位不同而有差異。結論：使用CT對運動中物體做影像掃描，其形狀集體機會因假體大小、密度、運動週期、及使用來繪製輪廓之CT值而有差異，這些現象在臨床上治療胸腹部病人時必須加以考慮並審慎評估其對放射治療劑量之影響。

Respiration during radiation delivery increases the uncertainty of therapeutic doses. In order to assess the effectiveness of treatment correctly, evaluation and management of respiratory motion effect are essential in clinical radiotherapy. The purpose of this study aims the volume variation while acquiring the images of moving objects. We design a moving phantom moving in simple one-dimensional harmonic motion to simulate the target motion during radiation treatment. The phantom includes motor gear system and three different ball phantoms with specific size and density. The images were acquired with tradition spiral CT and sorted in phase according to the scanning parameters. The contours delineation and calculation of ball volumes were performed in Eclipse treatment planning system. Base on the images sorting, the outlines of moving phantoms were observed in different phases. The results show the volume of ball phantoms depend on the size and density of phantom, the period of motion and the threshold HU value of auto-contouring. The phenomenon of volume variation provides useful information in the clinical radiotherapy.