放射治療的目的是使腫瘤細胞可以得到最高的劑量，而周圍正常組織所受到的傷害可以減至最低。為了達到此理想，治療儀器及技術也不斷的發展以及改進，然而也提高了對治療誤差的敏感度，所以必須減少治療誤差以減少正常組織的傷害。治療誤差主要的來源有兩個：設定誤差及器官位移。設定誤差即病人治療位置誤差；器官位移所造成的誤差是因為呼吸、心跳、吞嚥、胃腸蠕動等造成器官位置或形狀的改變。而其中以呼吸所造成的器官位移影響最大，如腹部腫瘤可能因此位移3公分。為了解決此問題，所以近來發展了一套呼吸同步放射治療系統，使治療時射束可以隨著病人呼吸進行調控，當腫瘤到達某一位置時再進行照射，因此可以減小安全邊距以及正常組織的劑量。而本研究著重於此系統的評估，主要分成三部分：發展影像處理系統自動追蹤橫膈膜位移、比較橫膈膜和皮膚移動之間的關係、利用腫瘤控制機率及正常組織副作用機率來評估呼吸同步治療系統的可行性。
在評估影像處理系統可行性方面，與人工定位系統比較結果，誤差為1.06±1.25 mm，此誤差相對於呼吸所造成的誤差來說仍在容許範圍內，所以此系統可用於臨床上。在探討皮膚與橫膈膜移動之間的關係方面，發現它們之間有時間差，但由於目前臨床資料不夠多，所以它們之間的關係尚不清楚。而在評估呼吸同步放射治療系統可行性方面，目前只評估一位肺癌病人，其結果顯示，呼吸調控可以減少安全邊距以及正常組織副作用機率。從目前結果看來，呼吸同步放射治療系統在臨床上的可行性很高，而且若真的能用於臨床上，對於治療胸部或腹部腫瘤將有很大的助益。

The goal of radiotherapy is to deliver as much dose to the tumor as possible while sparing surrounding normal tissues from radiation toxicity. The goal can be achieved by the continuous advancement of new treatment technology. On the other hand, these developments would also lead to increasing sensitivity to treatment uncertainties, mainly due to setup error and organ motion. Setup error is also called patient positioning error, deriving from everyday treatment variation. Organ motion could be caused by breathing, heartbeat, swallowing, and peristaltic motion. Organ motion caused by breathing has the largest impact on treatment accuracy. To solve this problem, a respiratory gating device which could deliver radiation treatment synchronized with patient breathing to reduce radiation toxicity to normal tissues is developed. The main objectives of this project are divided into three parts: developing new image processing software, finding the relation between skin movement and diaphragm displacement, and evaluating the feasibility of clinical respiratory gated radiotherapy by means of normal tissue complication probability and tumor control probability.
The difference of the traced position of diaphragm between the automatic image tracing software and manual tracing was 1.06±1.25 mm and was much smaller than the average displacement caused by breathing. The result suggested that image processing system can be used in clinical settings. Time delay was observed when comparing the respiratory patterns of skin movement and diaphragm displacement. However, due to insufficient patient data, the relationship between these two movements is still indecisive. In evaluating the clinical feasibility of the respiratory gating system, one patient with lung cancer was taken as a demonstrative case. The result showed that respiratory gating treatment can diminish safe margin and normal tissue complication probability. This example has demonstrated the feasibility of clinical application of this system.

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