射源皮膚距(SSD)與靶角度造成之跟效應變化

The Variation of Heel Effect Changed with Different Source-Skin Distances and Target Angles

陳拓榮(Tou-Rong Chen) ； 廖明雄(Ming-Hsiung Liao) ； 許文林(Wen-Lin Hsu) ； 李超群(Chau-Chin Lee) ； 魏嘉賢(Chia-Hsien Wei) ； 葉善宏(San-Hung Yeh)

《中華放射線技術學雜誌》 28卷1期 (2004/06) Pp. 59-68

https://doi.org/10.30045/CJRT.200406.0007

摘要

實驗以熱發光劑量計評估六種不同的射源皮膚距離（SSD, source to skin distance）與二種不同靶角度對跟效應的變化。熱發光劑量計採用輻射防護協會與清華大學二批不同之劑量計。結果顯示在整個X光暴露照野內，相對的跟效應變化比率不會因SSD距離的改變而有太大的改變。所以若考慮被照物體和照野的相對大小，可選擇較大的照野，即相對地較大的SSD作為照射條件，以減少跟效應的影響。另外，使用清華大學之熱發光劑量計（TLD-100），各層間TLD度量到的實驗值變化較大，此應肇因於輻防協會是以二點TLD的平均值來評估X光暴露，而清華大學TLD有限，故僅以一點評估，所以誤差較大。四組結果顯示，本校放射技術系實驗室的Bennett X光機，其陰陽極兩端X光強度相差27~28％；而Siemens X 光機陰陽極兩端X光強度相差24~26％。Bennett X光管14° 的靶角度略小於Siemens X光管16° 的靶角度，應是造成Bennett X光管跟效應較Siemens X光管略為嚴重的主因之一。我們也發現在中心點到陰極端間的各點，強度改變較小，四組差異僅2~6％；而中心點到陽極端的強度則改變頗大，差異達20~24％。

關鍵字

跟效應 ； 靶角度 ； 熱發光劑量計

並列摘要

The thermoluminesent dosimetry (TLD) was adopted to assess the variation of heel effect. Six kind of source to skin distance (SSD) and two type of target angle were analyzed. The TLD were provided by National Tsing Hua University (NTHU) and Radiation Protection Association (RPA) R.O.C., and two x ray machines, produced by Siemens and Bennett. The result showed the variation of heel effects is only a little changed with different SSD distances in the field of x-ray exposure. If the exposure object is large, large SSD that results in large exposure field is recommended, because using larger SSD as the exposure conditions will reduce the influence of heel effects. The experiment adopted one NTHU TLD and two RPA TLDs, respectively, to assess each space point. Obviously, using one NTHU TLD showed a larger fluctuation of readout data than that using two of RPA TLDs. The intensity of Bennett x ray tube between anode and cathode differs from 27% to 28%. That of Siemens x ray tube is smaller, from 24% to 26%. Because of the smaller target angle, 14°, of Bennett x ray tube than that of Siemens x ray tube, 16°, Bennett x ray tube revealed more serious in the heel effect than Siemens x ray tube. The variation of intensity in the cathode region, from center to cathode, is small. Four sets indicated 2% to 6% variation. But the other region, from center to anode, the variation of intensity is large. It changed from 20% to 24%.

並列關鍵字

heel effect ； target angle ； TLD