使用半值層來評估新竹區診斷X光機射束品質

The Methodology for Evaluating Half-Value Layer on the Diagnostic X-Ray Units

張榮華(Jung-Hua Chang) ； 魏伯翔(Bo-Xiang Wei) ； 黃沈隆(Shen-Long Huang) ； 朱佑羚(Yu-Ling Chu) ； 秦作威(Trow-Way Chin)

《加馬》 42期 (2011/06) Pp. 27-32

https://doi.org/10.30173/JG.201106.0004

摘要

目的：使用半值層(half-value layer, HVL)來評估診斷X光機射束品質。由於電腦放射攝影(Computed radiography, CR)、數位放射攝影(Digital Radiography, DR)系統已普遍使用於各醫療院所，而CR、DR系統於攝影後可以自動或手動來進行影像調整修正，本研究的目的為瞭解新竹地區各醫療院所使用半值層來評估X光機射束品質。方法：本研究以NERO(上標 TM) mAX Model 8000、FLUKE Victoreen 4000、以新竹區域六部單φ與五部項3φ，共11部X光機來進行評估，SID位置固定為100cm，並固定準質儀的10×10平方公分大小來進行量測。結果：在單φ60kV~120kVp量測中，其HVL的變動範圍為2.28~6.3(mm Al)。3φ60kV~120kVp量測中，其HVL的變動範圍為2.43~6.95(mm Al)。11部X光機的HVL標凖差SD的變動範圍為45~0.89(mm Al)。結論：由於半值層的厚度影響著射來品質。如果半值層愈大，表示射束硬化的程度越高。所以要了解射束品質，則必須知道射束的半值層厚度，因此從半值層的厚度來判斷射束的品質，半值層越大，表示低能量的光子越少，射束的品質越好。如此，將不會增加病患的皮膚劑量。因此瞭解射束品質來確保降低病人的醫療輻射劑量，以HVL的量測評估既方便也非常實用，並也符合ICRP合理抑低as low as reasonably achievable (ALARA)之精神。

關鍵字

半值層 ； 射束品質 ； 濾片

並列摘要

Objective: In this study, half-value layer (HVL) was used to evaluate the diagnostic X-ray beam quality. As computer radiography (CR) and Digital Radiography (DR) system have been widely used in various medical institutions, images can be subjected to auto exposure control (AEC) or manually adjusted or amended The purpose of this study is to assess the X-ray beam quality in the medical institutions of Hsinchu area using HVL.Methods: NERO(superscript TM) mAx Model 8000 and FLUKE Victoreen 4000 were used to study the half-value layer and tube voltage. The beam output (10×10 cm^2) and sources to image distance (100 cm) were fixed for the assessment of 11 x-ray units, of which 6 units arc equipped with single phase and 5 with inverter frequency power supply.Results: The measurement of HVL was deviated between 2.28 to 6.3 mm Al from the units with single phase power supply and between 2.43 to 6.95 mm Al from those with inverter frequency power supply.Conclusions: The half-value layer thickness affects the beam quality. The larger half-value layer represents the higher degree of beam hardening, causing a reduced skin dose of the patients. Therefore, understanding the beam quality can ensure that lower radiation doses are received by the patients from medical care. HVL measurements and assessments are very convenient, practical and reasonable, and are also in line with the spirit of the ICRP principle-as low as reasonably achievable (ALARA).

並列關鍵字

half-value layer ； beam quality ； filtration