運用田口最佳化於新建立多元智能刀(Radixact)放射治療中心的環境劑量之TLD讀取條件

中山醫學大學附設醫院設立多元智能刀(Accuray® Radixact®)提供病患精確的放射治療，新儀器確保劑量更緊貼腫瘤靶區，更有效地降低重要器官所受的劑量。為期六個月的研究中，使用熱釋光劑量計 (TLD) 方法評估 Radixact 設施的環境輻射。使用 6 MV 光子校準 TLD-100H。為了優化 Harshaw 3500 讀取器 TLD-100H 發光曲線的淨計數，使用田口法對 TLD 進行了分析。組織六種最佳化條件的十八種組合。將三個水平中的每一個分為18組，根據L18(21×37)直交表收集訊號雜訊比(S/N)。最佳化結果為（1）儲存溫度26℃（2）升溫速率5℃/s（3）預熱溫度135℃（4）最高溫度240℃（5）預熱時間8 s（6）間隔時間24小時。訊號雜訊比從先前的設定-5.21 dB 快速增加到最佳化設定的-2.56 dB。六個月內環境輻射的主要且相對顯著的變化為機架頭頂部的1250 ± 200 mSv/mo和治療室最遠處的15.1 ± 0.10 mSv/mo。治療室的半值層接近1.61 ± 0.16 m，最後確定了最小可偵測劑量為35.9 nC，以證明TLD-100H方法的可靠性。此外，我們評估了Pb/PE滑動門外部和非控制區域的散射劑量幾乎等於背景輻射。

To evaluate environmental radiation of Radixact facility using thermoluminescent dosimeter (TLD) approach during six-month survey. First, TLD-100H was calibrated using 6 MV photons. Second, to optimize the net counts of glow curve of TLD-100H of Harshaw 3500 reader, TLDs were analyzed using the Taguchi optimization method. Eighteen combinations of six optimized conditions were organized. Accordingly, each of three levels were organized into 18 groups to collect the signal to noise (S/N) ratio according to L18(21×37) orthogonal array. The optimization results are (1) storage temperature 26℃ (2) heating rate 5℃/s (3) preheat temperature 135℃ (4) maximum temperature 240℃ (5) preheat Time 8 s (6)interval time 24 hours.The S/N increased rapidly from the previous setting of -5.21 dB to the optimized setting of -2.56 dB. The major and relatively significant variations in environmental radiation varied from 1250 ± 200 mSv/mo at the top of gantry head and 15.1 ± 0.10 mSv/mo at the farthest place of treatment room during six months. Half value layer of treatment room is nearly 1.61 ± 0.16 m, Finally, the minimum detectable dose was also identified to demonstrate the reliability of the TLD-100H approach. In addition, we evaluated that scattered doses outer part of Pb/PE sliding door and uncontrolled area are nearly equal to background radiations.