目的：強度調控放射治療(intensity modulated radiotherapy; IMRT)利用非均勻強度射束，可以中準確的把所需的放射線劑量給到腫瘤體積上。然而治療中由於器官的運動，原本預期之劑量分布會有扭曲而失真。本研究係針對呼吸運動，發展呼吸同步之放射治療法。材料與方法：我們以視覺上的週期圖案來誘導病人呼吸，使其呼吸週期固定。藉此吾人可預測治療期間病人呼吸的相位，而器官的位置可經由透視預先得知。並且修改多葉準直儀(multileaf collimator; MLC)的控制檔案，來修正各個葉片(leaflet)移動的速率以改變射束方向，使射束隨著呼吸同步運動，如此便可將照野固定在腫瘤之上，減少呼吸運動所造成劑量分布的扭曲。結果與討論：我們以假體模擬呼吸運動，以EDR2驗證片做劑量分布的測量。結果顯示改變MLC的運動模式可以用來減少呼吸運動所造成的失真。利用週期圖案來誘導病人呼吸，也可達到運動規律化的效果。本方法可以運用在臨床上，它比其他呼吸運動修正方法的好處是治療時間不會延長。不過它需要病人的合作，使得呼吸運動能夠規律的進行。

Purpose: Intensity modulated radiation therapy (IMRT) utilizes nonuniform beam profile to provide desired radiation dosage to the tumor volume more accurately. However, the problem of intra-fraction organ motion can cause distortion to the desired beam intensities. This study aims to develop a respiration adaptive technique to toggle the problem of respiratory motion in radiation therapy. Materials and Methods: A video cue that shows a cyclic moving pattern is shown to the patient to help adjust his respiratory motion. Once the respiratory motion becomes regular, we can predict his respiratory phase during the treatment. The trajectory of the organ due to the respiratory motion can be obtained from the fluoroscopy study. The trajectory is then used to modify the velocities of MLC leaves so that the radiation field is synchronized with organ motion. Once the beam moves with the respiratory motion, the field size can be fixed on the tumor volume and reduce the distortion of dose distribution due to the organ motion. Results and Conclusions: A phantom was built to simulate the respiratory motion. EDR2 films are employed for the measurement of dose distribution. Preliminary results show that modification of MLC can be used to reduce the distortion due to respiration. Visual cue can be used to improve the regularization of respiration. This technique can be applied to clinical cases. The advantage of this Respiration Adaptive IMRT is to eliminate the inaccuracy of the TM field delivery caused from respiration movement without the cost of treatment efficiency. It requires patient's cooperation for regular respiratory motion.