目的：利用氣泡偵檢器量測Siemens PRIMUS直線加速器15MV光子與不同能量電子之中子污染量。材料與方法：不同靈敏度的氣泡偵檢器分別佈點於治療室內病人平面的位置，距離等中心處不同距離。量測15 MV光子40×40cm2與0×0 cm2及15、18與21 MeV電子25×25 cm2電子錐照射下治療室內之中子等效劑量分佈情形。結果：治療室內中子等效劑量量測結果發現該量隨距離等中心越遠而遞減，最大值發生在等中心處，對15 MV光子40×40 cm2與0×0 cm2分別為184.3±9.0及16.99±5.99 mRem per Gy x-ray，對 15、18與21 MeV電子25 x 25 cm2電子錐照射下，該值分別為10.00 ±2.04、26.27 ±6.12及34.90 ±2.96 mRem per Gy -electron。能量小於12 MeV之電子的中子污染小於氣泡偵檢器之偵測極限。結論：氣泡偵檢器於本量測研究中呈現穩定、方便與準確之特性，適合於此量測所需。中子等效劑量隨距離等中心越遠而遞減，並隨電子能量增加而遞增。本量測結果尚不足做為病人治療時中 子污染評估之用，後續假體內之量測工作是必須的。

Purpose: Measuring the photoneutron contamination of 15 MV X-ray and various electrons emitted from Siemens PRIMUS linear accelerator by using bubble detector. Materials and Methods: Various bubble detectors are arranged around the linac head with the interval of 1m and the same height of isocenter to measure the dose equivalent distribution in the treatment room. The measurements were perform for 15 MV x-rays with 40×40 cm2 and 0×0 cm2 fields and for 15, 18, and 21 MeV electrons with 25×25 cm2 electron cone. Results: Neutron dose equivalent rate in the points of measurement in the treatment room decreased with increased distance to isocenter. The maximum neutron dose equivalent are at isocenter, and its values for 15 MV 40×40 cm2 and 0×0 cm2 are 184.3±9.0 and 16.99±5.99 mRem per Gy x-ray, respectively. The values for 15, 18 and 21 MeV electrons with 25×25 cm2 cones are 10.00±2.04,26.27±6.12 and 34.90±2.96 mRem per Gy-electron, respectively. The neutron contamination of electron less than 12 MeV is under detection limit. Conclusion: Bubble detector performs the stable, convenient and accuracy properties in this photoneutron measurement. The neutron dose equivalent decreased with increased distance to isocenter. With electron energy increased, the neutron contamination also increased. Further studies of in-phantom measurements are required for the evaluation of the neutron dose equivalent in the patient.