本文探討呼吸運動對放射調控技術(非旋轉式與旋轉式)之劑量與輻射生物效應之影響.研究方法其一以呼吸運動與準直儀之運動(非旋轉式IMRT)作旋積.對旋轉式IMRT則應用4DCT影像配準之□果評估呼吸運動對劑量之誤差.

旋積方式產生等效強度分佈以代表呼吸運動對原強度分佈之扭曲.此方法對108個強度分佈受扭曲後之結果作統計分析,結果發現扭曲之大小與呼吸運動範圍d,強度梯度G,與d*G有較大之相關性(相關係數分別為0.6,0.56,0.9).

以4DCT的形變配準技術對旋轉式調強分析劑量誤差,結果顯示在呼吸運動範圍1.5公分內,劑量誤差非常有限.以高調強計畫而言,1.5公分之呼吸運動僅造成最大3%的期望誤差偏離.此結果顯示旋轉式調強技術同時適用單次與多次放射治療.

論文以等效均勻劑量方法評估呼吸運動的輻射生物效應.透過肝內腫瘤細胞對輻射線之存活率分析,本論文研究臨床肝內腫瘤治療之適應治療照野大小.

This dissertation investigates the dosimetric and radiobiological impact of respiratory organ motion on the delivery of IMRT techniques for intra-hepatic tumor. There are two methods applied in two different IMRT techniques. Convolution incorporated motion trajectory was performed to study motion impact in fixed-beam IMRT technique. A method incorporated 4DCT data was utilized to evaluate motion impact in rotational IMRT technique. The 4DCT method used a diffeoremorphic registration as framework to construct deformation field in three dimensions.

The convolution method generates effective fluence which is the fluence distorted by the motion function. By analyzing 108 fluence generated from fixed field IMRT, this study found there are strong correlation of intensity error with motion displacement d (0.6), fluence gradient G (0.56), and their multiplication d*G (0.9). To keep the average intensity error below 0.05 and 0.03, the maximum motion displacement should be smaller than 1.3 cm and 0.7 cm, respectively.

With 4DCT data, dosimetric error due to deformation is intrinsically included. Study from two cases showed that the dosimetric error due depth changes alone were 3% and 1%, respectively. Comparing the motion effect on the delivered dose between the moderately modulated plans and the highly modulated plans for the two cases in this study, the latter only increases the maximum dose deviation from the expected dosimetric error by 2% (from 1% to 3%). Method was applied at single-arc IMAT in this study, the same scheme can be applied at multiple-arc IMAT as well.

Radiobiological impact of the respiratory motion was evaluated with the concept of equivalent uniform dose. Through the correlation between the survival fraction and different clinical cell type or stage of intra-hepatic tumor, appropriate margins were designed to account for the biological impact from respiratory motion in IMRT delivery.

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