胸部X光劑量評估研究

Dose Estimation of Chest X-ray Examinations

游澄清(Cheng-Ching Yu) ； 許芳裕(Fang-Yuh Hsu) ； 褚珮琇(Pei-Shiu Chu) ； 欒冰心(Bin-Chin Luan) ； 朱國繁(Kuo-Fan Chu) ； 林招膨(Jao-Perng Lin)

《中華放射線醫學雜誌》 28卷2期 (2003/04) Pp. 91-96

摘要

本文主要在探討胸部X光診斷所造成的輻射劑量。其目的，在於研究X光機的操作因子對診斷劑量的影響，並探討如何利用現有的各項設備來提昇胸部X光片的可判讀率，並合理抑低病人劑量。本研究使用壓克力假體及熱發光劑量計(TLD)，探討X光機的各種操作因子與病人入射表面劑量(ESD)的關係。藉由醫院例行胸部X光檢查的機會，以TLD實測病人ESD，作為病人劑量評估的參考依據，改變X光機的操作條件，研究提昇X光片的判讀率並合理抑低病人劑量的方法。研究結果發現，入射表面劑量隨操作條件而變，以相同的條件照射，三相位X光機所造成表面劑量大約是單相位X光機的1.9倍；入射表面劑量與kVp的2.2至2.5次方成比例，與mAs約成線性正比，與焦斑至底片距離(FFD)的關係大約符合平方反比定律；照野面積及身體厚度雖會影響表面劑量的大小，但其程度遠低於kVp及mAs的影響。實驗結果證實，在臨床上藉由適當改變X光機的操作條件，的確可以改善X光片的判讀率並合理抑低病人劑量。實驗結果也顯示，使用改善之後的胸部攝影條件，病人實測的入射表面劑量為0.12±0.06 mGy，小於NRPB與IAEA建議的參考劑量，滿足劑量約束化的要求。

關鍵字

熱發光劑量計 ； 表面劑量 ； 防護最適化

並列摘要

The work of this paper is to estimate the dose produced by the examinations of chest x-ray. Impacts of operation factor of x-ray machines on diagnostic were estimated in this paper. The way of increasing determination rate and decreasing patient dose was discussed. PMMA phantoms and TLDs were used in performing the estimation of the relationship between operation factors and entrance surface dose, ESD. TLDs were also used in clinical chest x-ray examinations to get the ESD of 90 patients. The results show that ESD depends on operation factors. Under the same irradiating conditions, the ESD ratio of three phase unit x-ray generator is about a factor of 1.9 times to single phase unit. Both of the ESD were proportional to kVp 2.2 to kVp 2.5 and were linear proportion to mAs. Inverse square law exists in the relationship of focus-film distance, FFD, and ESD. The impacts of field size and patient thickness to ESD are negligible. Optimized operating condition is chosen to improve the diagnosis rate and to reduce the patient dose. The ESD, 0.12±0.06 mGy, performing the optimized operating condition of chest x-ray examinations, is less than both values of reference doses recommended by NRPB and IAEA.
By chest x-ray films of 90 median-sized patients, finally 100 kVp film showed satisfied structure illustration. The 90 kVp films were underexposured and could not show the anatomic structures; the 110 kVp films were overexposured, the detailed structures disappeared, only bony structures and heart could be seen. So that 100 kVp film is the best of choice.

並列關鍵字

TLD ； Entrance surface dose (ESD) ； Optimized dose limit