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題名 | 電腦斷層治療機照野寬度與螺距參數設定對治療計畫的影響:假體實驗=The Influence of Field Width and Pitch in Tomotherapy Plan: Phantom Study |
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作者 | 吳任弘; 葉恬綺; 溫嘉綺; 王雱儀; 蕭仟翊; 許仲賢; | 書刊名 | 放射治療與腫瘤學 |
卷期 | 21:2 2014.06[民103.06] |
頁次 | 頁131-140 |
分類號 | 414.93 |
關鍵詞 | 電腦斷層治療; 螺距; 漣波效應; 放射治療計畫; Tomotherapy; Pitch; Ripple effect; Radiotherapy plan; |
語文 | 中文(Chinese) |
中文摘要 | 目的:電腦斷層治療機(Tomotherapy®)以旋進(helical)方式傳遞劑量,因此照野寬度(field width)與螺距(pitch)兩個參數的設定,會對治療計畫的結果產生一定之影響。本實驗目的在比較不同的照野寬度與螺距設定,在均勻假體中對治療計畫結果的影響。材料與方法:以電腦斷層掃描儀取得圓柱型固態水假體(Med Cal, Verona, WI)之斷層影像。繪製靶體積與危急器官輪廓、執行相同的最佳化疊代次數與相同的靶體積與危急器官權重,僅設定不同照野寬度(5 cm、2.5 cm、1 cm)及螺距參數(0.2、0.4、0.6、0.8)。比較整體時間、靶體積之均勻指標與頭腳向之漣波效應(ripple effect)以及危急器官接受的劑量。結果:結果顯示當機頭旋轉一圈所花週期大於最快週期時,照射時間與螺距值無關而與照野寬度 有關,5 cm、2.5 cm、1 cm所需的照射時間比值約為1:1.8:4。當螺距太小,使得機頭旋轉週期小於15秒時,為配合機器最快週期的限制,旋轉週期會延長為機頭的最快週期,使照射時間增長。照野寬度愈大頭腳向劑量半影區愈大。螺距設定0.6時靶體積內有明顯的漣波效應,此時靶體積的均勻度最差。靶體積順形度在橫切面上並無明顯差異,照野寬度愈小在照野邊緣頭腳向的劑量梯度愈大。小照野寬度與小螺距對危急器官的保護最佳。另均勻假體內,落在AP方向的危急器官接受的平均劑量比側向高。討論:由結果可得照射時間與照野寬度有明顯相關,若以治療時間為主,可考慮用大照野寬度搭配小螺距,但位於靶體積外側頭腳向區域的劑量會增加。若以計畫品質為主,則使用小照野寬度與小螺距,但治療時間會增加。 |
英文摘要 | Purpose: Field width (FW) and pitch factor (PF) are parameters that influence the quality of treatment plans and beam-on times in Tomotherapy that delivers helical radiation therapy. This study examines the relationship between these parameters and their influence on the quality of treatment plan. Material and Method: Target volumes and organ at risk (OAR) volumes were delineated on a computerized tomography of a cylindrical chess phantom. Maintaining the weightings of each volume, treatment plans were optimized with a different combination of planning parameters (FW = 5, 2,5, 1 cm. PF = 0.2, 0.4, 0.6, 0.8). Each plan was analyzed for dose distribution, treatment time, homogeneity index, conformity index and ripple effect. Result: For revolutions lasting between 15 and 60 seconds, the increase in treatment time correlated with decreasing field width. The ratio between treatment time with different field widths, when treatment time at 5 cm was 1, 1.8 and 4 times at widths of 2.5 cm and 1 cm respectively. Where change in pitch factor was did not result in change in treatment time. For revolutions under 15 seconds, smaller pitch denotes longer treatment time. The dimension of penumbra increased with increasing width. At pitch factor 0.6, the ripple effect was evident and the homogeneity index was at its worst. Transversely, conformity indices differed non-significantly. Longitudinally, the dose gradient increased with decreasing field width. Doses to OARs were minimized at small pitch and field width. OARs in longitudinal direction had higher median dose. Conclusion: Change in field width could lead to change in treatment time. Treatment time could be shortened with combination of large field width and the pitch value, at expense of increased dose to longitudinal directions. Combination of small field width and small pitch yielded better planning quality, and increase in treatment time. |
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