硫酸亞鐵膠體劑量計在放射治療應用之原理與探討

The Study of Ferrous Sulphate Agarose Gel Dosimetry in Radiation Therapy

羅濟慶(Chi-Ching Lo) ； 李俊信(Jason J.S. Lee)

《放射治療與腫瘤學》 4卷2期 (1997/06) Pp. 139-145

https://doi.org/10.6316/TRO/199704(2)139

摘要

目的：探討硫酸亞鐵劑量計之原理，並研究其磁振T1鬆弛率與吸收劑量之間的關係，並分析其在人體組織內吸收劑量反應與分佈的情形，最後也針對其在臨床放射治療應用上之可行性做一嘗試與比較。
材料與方法：配製硫酸亞鐵溶液於洋菜粉末中，隔夜並待凝固後，置入線性加速器照射，最後經由磁振造影求出其T1鬆弛率，並進而研究其T1鬆弛率與吸收劑量之間的關係。同時也製作乳房相似假體與非均質組織來模擬肺部空腔假體，以分析其劑量分佈的情形，也與電腦治療計劃做一比較及分析。
結果：硫酸亞鐵劑量膠體在磁振T1鬆弛率與劑量反應。在劑量達30 Gy時仍呈直線關係。但由於磁振主磁場不均勻、膠體內離子擴散及降解作用等因素使得其信號與雜訊比仍未十分滿意。
結論：硫酸亞鐵劑量計在三度空間立體劑量分佈上非常有用，尤其在乳房與胸腔壁間之劑量分佈、組微密度不均勻之介面劑量分析上，有其臨床上應用的價值。但在提昇影像解析度、信號與雜訊比方面，仍有待更進一步的研究。

關鍵字

硫酸亞鐵膠體 ； 放射劑量計 ； 放射治療

並列摘要

Purpose: To study how the ferrous sulphate agarose gel reports the dose response and distribution to the mediums. The potential applications to clinical radiation therapy are also introduced.
Material and Method: Ferrous sulphate agarose gel containing ferrous ammonium sulfate, sodium chloride, sulfuric acid and triple distilled water was employed to measure dose distribution in the mediums. The change for T1 of the spin-lattice relaxation rates of ferric ions with an MRI scanner was studied as a function of absorbed dose given to the gels. Breast-mimic gel phantom and inhomogeneous layer phantom were constructed to compare the 3D dose distributions in the gel phantoms with treatment planning dose distributions in these phantoms.
Result: The dose response of the gel is linear up to 30 Gy. The degree of homogeneity of the magnetic field, chemical diffusion and degradation of the gel are the major factors affecting the signal to noise ratio of the gel imaging.
Conclusion: The gel may he applicable to 3D dose verification in the areas of bone and air interface, breast and chest wall. However, the signal strength and resolution of the gel images are still not clinically satisfactory. Further studies to improve the above insufficiencies are needed.

並列關鍵字

Ferrous sulphate agarosc gel ； Radiation dosimeter ； Radiation therapy