輻射生物實驗細胞照射之劑量分析

目的：基礎輻射生物學的細胞照射實驗對放射生物學的發展影響深遠，利用直線加速器做生物細胞照射。受限於培養細胞之器皿的幾何結構，在劑量上有相當多的不確定性。實際以TLO量測各種照射條件的劑量值，以求準確地控制劑量的給予。材料與方法：本研究使用ELEKTA SL-18直線加速器所產生的6 MV、10 MV光子射束及10 MeV、12 Mev、15 Mev電子射束，照野大小設定光子射束為20×20平方公分，電子射束為25×25平方公分。選擇三種常用於輻射照射實驗的細胞培養皿，實驗的架設依照射束照射方式分成AP和以兩部分，皆使用光子和電子射束。劑量量測以厚度0.1 mm的超薄TLD執行。細胞照射實驗的情況類似於體內不均勻介質分布，劑量分布在此非均質組緞的後面則可以利用等效厚度係數的方法評估。嘗試建立不同形式培養皿、射束能量及照射條件所造成劑量計算值與量測值的關係。結果與討論：AP照射的情況下，光子射束的量測值有高於計算值的趨勢，6MV偏高約：7%；10MV則為5%；電子射束在10 MeV、12 MeV下，計算與量測值相當吻合，差異約在±3%以內。但是在15 MeV時，量測值則略高於計算值。於PA架設模式下，量測值普遍呈現低於計算值，尤其能量高的光子射束或空腔較大的培養皿更為明顯。高能光子較電子射東有更明顯的增建區域，當劑量評估區域落於增建區，光子射束可能會有較高的劑量不確定性。高能電子射束；10、12、15 MeV等的PDD曲線在深度為1cm~3.5cm之間時，呈現一個較為平坦的最大劑量分為區域。即使在空腔厚度評估準確性上有些不足，但是因為處於平坦區，劑量給予的誤差將較小。

關鍵字

細胞照射；界面劑量； TLD ；等效摩度係數CET

並列摘要

Purpose: Dose analysis is important for biological cell irradiation study. When cell irraiation was performed by using a high energy radiotherapy Linac, the dose uncertainties caused by the inhomogeneity structures of the cell containers make it difficult to estimate the cell dose. In this study, cell doses were measured and analysised for different setup conditions. Materials and Methods: 6 MV, 10 MV photon beams and 10 MeV, 12 MeV, 15 MeV electron beams generated by Electa SL-18 Linac were used in this study. Field sizes of 20×20 cm^2 for photon beams and 25×25 cm^2 for electron beams were designed to have a fully side scatter condition. Dosimetry analyses for AP and PA directions were performed for 86 mm×l9.5 mm Polystyrene petri dish, 25 cm^2×24.3 mm and 75 cm^2×36.5 mm Tissue Culture Flask. Extra thin TLDs (0.1 mm) were used for dose measurements. The cell irradiation condition is similar to the inhomogeneity distribution in a human body. GET (Coefficient of Equivalent Thickness) is used to evaluation the dose distribution which beyond the inhomogeneity structures. The dose variations for calculation and measurement were analyzed in different setup conditions. Results and Discussion: In AP setup, the calculation dose was consistent for electron beams, within 3%, but was under estimated for both of photon beams, maximum variation of 7% in 6 MV and 5% in 10 MV. In PA setup, the calculation doses were under estimated for electron and photon beams, and are more significant for higher photon energy and larger air cavity. The depth dose distribution in buildup region is much sharper for photon beam than electron beam. This behavior makes a smaller dose variation in electron beams than in photon beams when evaluated position is located at the buildup area.

並列關鍵字

Cell irradiation ； Interface does ； TLD ； GET

國際替代計量

輻射生物實驗細胞照射之劑量分析

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