Gafchromic EBT2 膠片近幾年來在放射治療品質保證扮演著相當重要的角色。本實驗之目的在對Gafchromic EBT2 膠片做一系列的特性校驗，利用量測表面劑量及最大深度劑量，觀察在不同參數條件設定下其穩定度及再現性。利用不同臨床參數設定：包含Source to axis distance (SAD)、射束角度、照野大小、分次劑量照射、尺寸膠片、Region of interest (ROI)圈選方式及掃描時間，探討於不同條件下量測值之變化。在不同SAD下，其量測到表面劑量(d0)與最大深度dmax)劑量之比值(d0/dmax)差異變化約2%~3%；不同射束入射角度下，其量測比值(d0/dmax)平均差異約 1~2%。而照野大小改變方面，其量測比值(d0/dmax)因散射關係使其量測值會隨著照野大小增加而增加。在不同分次照射、EBT2 膠片尺寸、ROI 圈選方式之實驗下，表面和最大劑量深度下之改變其變異係數皆小於3%。掃描天數改變的實驗發現，若暴露後在7 天內掃描分析，表面(d0)和最大深度dmax)之量測值逐漸增加至5.57%及5.97%，7-14 天後則趨於穩定。由上述結果可得知GafChromic EBT2 膠片其穩定性和再現性是可信賴的，不同條件下量測值之變異程度皆小於3%，適用於臨床劑量驗證及輻射度量。

The recently introduced Gafchromic EBT2 film plays an important role in the quality assurance of radiation therapy.This study aims to analyze the stability and reproducibility of the Gafchromic EBT2 film under various clinical conditions.Different experimental parameters were set, including the source to axis distance (SAD), beam angle, field size, fractionsof irradiation, film size, the region of interest (ROI) selected, and scanning time. The measurements of the depths of thesurface dose (D0) and maximum dose (Dmax) were recorded and analyzed to study the differences in these measurementsunder the different conditions. Under different SADs, the difference in the ratio of the surface and maximum dose depths(D0/Dmax) is around 2-3%. Under different beam angles, this difference in D0/Dmax is around 1-2%. Further, D0/Dmaxincreases with the field size owing to the increase in the scatter dose. Under the various fractionations, EBT2 films sizes,or ROI selections, the CVs (coefficients of variation) of D0 and Dmax were all less than 3%. In addition, the results forthe first seven days of scanning time showed gradual increases in D0 and Dmax by 5.57% and 5.97%, respectively. After theseventh day, the change of measured values is becoming more stable. These results demonstrate the good stability andreproducibility of the Gafchromic EBT2 film under various conditions. The CVs for the measured values are less than 3%,which is suitable for clinical dose verification and measurements.