利用游離腔偵測器評估移動式X光機周圍劑量

Using Ion Chamber for Dose Assessment around a Medical Portable x-ray Unit

胡中昇(Jung-Sheng Hu) ； 李桂樑(Kuei-Liang Li) ； 楊枝哲(Chih-Che Yang) ； 黃姿婷(Tzu-Ting Huang) ； 林招膨(Jao-Perng Lin) ； 鄧世雄(Sai-Hung Tang)

《台灣應用輻射與同位素雜誌》 6卷4期 (2010/12) Pp. 954-959

https://doi.org/10.29832/TJARI.201012.0003

摘要

本研究評估本院放射科之醫療用移動式X光機在無鉛屏蔽條件下，所站位置至X光管之平行距離1公尺，兩個禮拜累積的劑量約爲0.044mSv，相當於年劑量0.528mSv，此值遠低於職業年限度值50mSv。而在有鉛屏蔽的狀況下，鉛屏蔽後方之醫護人員輻射劑量爲0.021mSv，換算成年累積劑量約爲0.2514mSv。X光管管套表面附近，劑量最大值位於X光管下方之X光射出窗附近，劑量值爲0.327mSv；而X光管上方因有外殼所以其輻射劑量偏低，僅爲下方射出窗周遭的約二十五分之一。X光管左右二端相差大，右端劑量值爲0.0676mSv約爲左端的五倍，主要可能爲陽極跟效應所導致。使用游離腔計數器評估醫用移動式X光機周圍空間的輻射劑量，包括實際現場的照射及模擬空間。在醫用移動式X光機周圍做游離腔計數器的放置，經實際照射病房現場累積約兩個禮拜的輻射劑量；空間的模擬則以醫用移動式X光機、假體、病床、計數器3D空間的放置，曝射50次以模擬現場照射及輻射劑量評估。
於X光室內空間曝露之模擬，鉛屏蔽離X光管球1.6公尺，鉛屏蔽前方劑量平均值爲0.0211mSv；而後方平均值爲0.0112mSv，鉛屏蔽約阻擋減少53%的輻射曝露。鉛屏蔽後方平均值0.0112mSv應可作爲50次醫用移動式X光照射曝露參考之保守值。而距離X光管0.5公尺、1.0公尺的劑量分別爲0.05044mSv、0.01643mSv，距離越遠輻射劑量越低。

關鍵字

曝露 ； 移動式X光機 ； 劑量 ； 游離腔計數器

並列摘要

The ion chamber dosimeter (Vitoreen 450P) was adopted to assess radiation dose that were resulted from exposure of medical portable X-ray machine. The study includes two parts, a field study and a laboratory experiment. The ion chamber dosimeter (Vitoreen 450P) the surface of an X-ray machine that was actually performed in the hospital and exposed to X-ray in one month. Besides, that a portable X-ray machine, a body phantom, and a table were assembled to setup on a clinical room and exposed 50 times to simulate the field study and investigate exposure strength.
The maximum accumulated dose around the surface of X-ray tube was 0.327 mSv that was found beneath the X-ray tube, near the window. But the dose that located upper the tube was low, a twenty-fifths of the maximum dose. Doses on the sides of the tube were rather different as a result of heel effect. The dose, 0.0676 mSv, on the right side is five times of that on the left side. The dose with a distance of 1.0 m from X-ray tube without any lead shield was 0.021 mSv for two weeks.
It is equivalent to 0.55 mSv for a year that is lower than annual occupational dose limit, 20 mSv. The exposure behind the lead shield was 0.021 mSv for two weeks. It is equivalent to 0.2514 mSv for a year.
The laboratory experiment was performed to simulate and assess space exposure around an X-ray machine. After fifty exposures, doses before and behind of lead shield were 0.0211 mSv and 0.0112 mSv, respectively. Lead shield prevents 53% X-ray exposure. The space exposures at the altitude of 1.0 m and was higher that at the altitude of 0.5 m. The exposures with a distance of 0.5 m and 1.0 m from the place to X-ray tube were 0.054 mSv and 0.0164 mSv, respectively. The data showed longer distance lower exposure.

並列關鍵字

Exposure ； Medical portable X-ray machine ； Dose ； Ion chamber meter