螺旋刀靜態式照野寬度與調變因子參數設定對放射治療鼻咽癌影響：侖道假體研究

目的：本研究目的在探討螺旋刀（Tomotherapy）執行電腦治療計劃優化演算，設定不同靜態式照野寬度（field width, FW）與不同調變因子（modulation factor, MF）參數設定，對於放射治療鼻咽癌各危急器官（organs at risk, OAR）劑量與治療時間的影響。材料與方法：依據鼻咽癌病例腫瘤位置，假想規劃計劃靶體積（PTV）與危急器官在侖道假體（Rando phantom）電腦斷層影像上。電腦治療計劃優化演算設定不同靜態式照野寬度（1.0 cm、2.5 cm和5.0 cm）搭配不同調變因子數值（1.0至5.0，每數值間隔0.2）組合，共設計63個電腦治療計劃。結果：靜態式照野寬度大小設定對於各危急器官劑量影響有顯著性差異（p ＜ 0.0001）。在電腦治療計劃各群組中（照野寬度1.0 cm、2.5 cm和5.0 cm），其調變因子數值設定分別小於等於1.8，左右兩側腮腺平均劑量會超過26 Gy耐受劑量限制標準；而設定為1.0時，脊髓神經與腦幹最大劑量會分別超過45 Gy與54 Gy耐受劑量限制標準。照野寬度大小會影響治療時間，1.0 cm、2.5 cm和5.0 cm各群組中所需的照射平均時間分別為1036秒、440秒和249秒。篩選出27個治療計劃執行劑量驗證，所量測的點劑量皆在±3%內；二維劑量分佈之γ指標（3%/3 mm）通過率介於90.1%～92.3%之間。結論：在臨床上若優先考慮降低危急器官劑量，優化演算的參數建議為設定照野寬度1公分搭配調變因子2.8，其次為照野寬度2.5公分搭配調變因子3.4，但照野寬度越小所需治療時間就越長。若考慮臨床病患無法長時間久躺時，可以選擇照野寬度5公分搭配調變因子數值為3.6。

關鍵字

螺旋刀；照野寬度；調變因子數值；鼻咽癌

並列摘要

Purpose: To study the influence of the static field width (FW) and modulation factor (MF) on the organs at risk (OAR) dose and treatment time of nasopharyngeal cancer by Tomotherapy. Materials and Methods: CT scan of RANDO phantom were used to prepare the radiotherapy treatment plan. Planning target volume and the organs at risk (OAR) corresponding to nasopharyngeal cancer were contoured in the CT scan. 63 Tomotherapy plans with the same parameter setting (importance and penalty) were obtained with static FW value including 1 cm, 2.5 cm, and 5 cm, combined with the different value of MF (range of 1.0-5.0 with step 0.2). Result: Treatment plan with different FW resulted a significant difference in the OAR dose (p ＜ 0.0001). For each computer plan group (FW 1 cm, 2.5 cm and 5 cm), average dose of the parotid gland was higher than the limit value (26 Gy) when the MF value is less than or equal to 1.8. When the MF value was set at 1.0, the maximum dose of spinal cord and brain stem were higher than OAR limits (45 Gy and 54 Gy, respectively). The treatment time with different FW (1, 2.5 and 5 cm) were 1036, 440, 249 seconds, respectively. In the 27 selected quality assurance (QA) plans, the measured dose point was within ± 3%. The gamma pass percentage (3%/ 3 mm) was between 90.1% and 92.3%. Conclusion: The clinical priority to reduce absorbed dose of critical organ, optimized algorithm with MF 2.8 plus a FW 1cm combination were suggested. The second choice combination was MF 3.4 plus FW 2.5 cm. However, small field width will significantly increase treatment time. Considering some patient could not lie down for too long, treatment time could be shortened with combination of MF 3.6 plus FW 5 cm.

並列關鍵字

Tomotherapy ； Field width ； Modulation factor ； Nasopharyngeal cancer

國際替代計量

螺旋刀靜態式照野寬度與調變因子參數設定對放射治療鼻咽癌影響：侖道假體研究

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