利用影像導引放射治療技術來評估擺位誤差對於計劃靶體積包覆率的影響

劉 義誠, 劉 煥彰, 陳 柏元, 陳 臣苑, 張 安進, 程 言鼎, Ngan-Ming Tsang, Ji-Hong Hong

Research output: Contribution to journalJournal Article peer-review

Abstract

目的:隨著科技日新月異,有愈來愈多先進的設備可供放射治療領域應用,本文主要藉著影像導引的技術並利用回溯分析的方式,評估頭頸癌病人若無經過影像導引,其位移修正對計畫靶體積 (PTV) 包覆率與周圍鄰近正常組織的體積被照射率的衝擊。 材料與方法:使用諾利刀直線加速器為二十位元病人進行影像導引放射治療,共三百八十六次的治療,利用影像導引系統(以人體骨骼為主配合×光影像融合)求出每次擺位誤差的位移修正,並以座標軸格式重新輸入治療計劃系統,但其他設定沿用舊治療計劃後取得新的治療計劃結果,利用計劃加總的方式,評估擺位元誤差對於計劃靶體積與正常組織之被照射率的影響。 結果:根據實際的測量結果,在前後軸位的平均位移修正為-0.4±0.9mm,而系統誤差標準差與隨機誤差標準差分別是0.9mm與0.9mm;在中側軸位的平均位移修正為-0.4±1.2mm;而系統誤差標準差與隨機誤差標準差分別是0.7mm與0.9mm;在頭腳軸位的平均位移修正為-0.1±0.7mm,而系統誤差標準差與隨機誤差標準差則分別是1.2mm與1.1mm。整體病人的空間向量位移小於3mm的頻率為88%,而平均位移間距是2.1±0.3mm。在腦部腫瘤與頭頸癌的病人之中V90(90%劑量曲線包含的體積)的錯失率分別為0.15%與0.17%;V95(95%劑量曲線包含的體積)的錯失率分別為0.37%與0.39%;僅有少於0.03%與0.31%的計劃靶體積被包覆在107%的高劑量區內。而在危急器官的體積被照射率的變異評估,腦部腫瘤病人左側眼睛、腦幹、右側眼睛的平均差異是0.25±1.36%、1.18±0.81%、-0.09±1.16%;頭頸癌病人的脊髓、左側腮腺、右側腮腺的平均差異則是-0.22±0.63%、0.15±0.77%、-0.21±0.80%。 結論:在進行治療計畫的規劃時,除了依van Herk.的建議在臨床靶體積的外緣多加2.5Σ±0.7σmm的安全間距外,依本研究所示,傳統治療擺位的誤差小於3mm的機會大約為88%,若可配合使用影像導引技術確認每次的擺位結果,則可控制每一次治療的擺位誤差低於3mm,讓空間向量的間距維持在5.2mm的範圍之內,進而相信實際治療時的臨床靶體積的包覆率與危急器官體積被照射之風險評估都在合理可接受的範圍內。
NTRODUCTION: By using image-guided correction, we analyzed the dose coverage of planning target volume (PTV) and surrounding normal tissues impacted by radiation dose retrospectively. This was done on head and neck (H&N) cancer patients who were not guided by imaging based on the effective treatment results of intensity modulated radiation therapy (IMRT). MATERIAL AND METHODS: 20 patients underwent image-guided radiotherapy (IGRT) resulted in a total of 386 paired images which were analyzed by software to acquire the correction shifts in three axis, followed by recalculation of a treatment plan system. The effect of PTV and normal tissue irradiation volume were evaluated by plan summation. RESULTS: The average correction shift of anterior-posterior (AP), medial-lateral (RL) and cranio-caudal (CC) directions were -0.4±0.9 mm, -0.4±1.2 mm and -0.1±0.7 mm, respectively. The systematic and random errors in AP direction were 0.9 mm and 0.9 mm, in RL direction were 0.7 mm and 0.9 mm, in SI direction were 1.2 mm and 1.1 mm. The average vector shift was 2.1±0.3 mm with 88% probability of being less than 3 mm. In brain and H&N tumor groups, the PTV missing probability of V90 (the volume covered by 90% isodose curve), V95 (the volume covered by 95% isodose curve) and V107 (the volume covered by 107% isodose curve) were 0.15% and 0.17%, 0.37% and 0.39%, 0.03% and 0.31%, respectively. On the other hand, in brain and H&N tumor groups, the probabilities of normal tissue being irradiated were as follows: 0.25±1.36% of left eye, 1.18±0.81% of brain stem, -0.22±0.63% of spinal cord, left 0.15±0.77% of parotid gland, -0.09±1.16% of right eye and -0.21±0.8% of right parotid gland. CONCLUSION: The dose coverage of PTV and normal tissue risk can be kept within the acceptable range by adding the safety margin recommended by Marcel van Herk (2.5Σ±0.7σ) mm along with the control of the setup error of less than 3 mm and the space vector shift of less than 5.2 mm.
Original languageChinese (Traditional)
Pages (from-to)125-135
Journal放射治療與腫瘤學
Volume17
Issue number2
StatePublished - 2010

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