目的：研究放射治療常用之XV和EDR2二種劑量驗證底片的特性與線性劑量反應範圍。材料和方法：由光密度劑量圖分析最適劑量區的範圍，並建議可應用之最適劑量反應區。另外評估劑量率、照野、深度、及X光能量，對XV和EDR2底片光密度的影響程度。結果：由H&D曲線圖知XV比EDR2底片的斜率大，而且達到飽和點的劑量值較小，這說明此底片可測量的劑量範圍較窄。在不同的劑量率照射下，EDR2底片與XV底片的光密度劑量曲線並無明顯差異。照野由5×5平方公分變化至20×20平方公分，對二種底片光密度之影響變化均小於1.5%。20公分的深度變化，對二種底片光密度之影響小於2.3%。X光能量從4 MV增至10MV，XV之光密度增加8.9%；而EDR2之光密度增加8.2%。結論：在10MV的X光曝露條件下，建議XV底片的最適劑量反應範圍在20~90 cGy；而EDR2底片之最適劑量反應範圍25~400 cGy。在光密度劑量圖之最適劑量區，EDR2底片的線性度較XV底片佳。在XV和EDR2底片的最適劑量區內，劑量率、照野、深度對光密度的影響小可忽略。但能量對光密度的測定，其影響不容忽視。

Purpose: To study the characteristics of two radiographic films and their linearly response ranges. Methods and Materials: Measurement and using the sensitometric curves to analyze the dose performance and recommend the best responsive range for XV and EDR2 films. The parameters of dose rate, field size, depth, and energy of x-ray were applied to evaluate the change in photographic density. Results Comparing the responsive region in sensitometric curves, the slope of XV film is larger than EDR2 film and the saturation dose of XV film is less than EDR2 film. It means responsive range of XV film is smaller than that of EDR2 film. The photographic density was lot changed with the dose rate. As the field size changed from 5×5 to 20×20 cm^2, the variation of four photographic densities was less than 1.5%. The change of photographic density was less than 2.3% within a depth form 5 cm to 20 cm. Replacing the energy of 4 MV with 10 MV, the density increased 8.9% for XV film and 8.2% for EDR2 film. Conclusion: We recommend the responsive range of XV film is from 20 to 90 cGy and EDR2 film is from 25 to 400 cGy, at the exposure of 10 MV x-ray. EDR2 film has a better linear relationship between photographic density and dose than XV film. No dose rate effect and a little change ill field size and depth were found. But, the x-ray clergy is an important parameter to the measurement of photographic density.