Simulation of in-vivo measurement of ^<90>Sractivity in bone by detecting bremsstrahlung x-rays

1)自60年代以来，已有大量的实验工作，<90><90>用装有NaI（Tl）晶体的全身计数器，在体外测量了~（18）Sr+~（18）Y的β射线产生的韧致辐射。利用内部蒙特卡罗程序SR90对~（133）Sr+~（133）Y的韧致辐射产额进行了定量评估<90><90>。2<137><40>）由大体积骨骼和薄皮肤组成的人体器官，如腿、腰和头，被认为是本目的的候选者。计算结果表明，由于腰部和头部含有大量的内部软组织，因此不合适。通过改变骨骼直径和皮肤厚度，研究了由骨骼和皮肤组成的同轴圆柱体近似的腿部体模。3）获得了进入直径为200 mm的探测器窗口的光子谱。本文引入信噪比s/n作为定量判断最佳体内测量条件的因子，s/n = &lt;@D_7I（&lt;@D190@&gt; D_1Sr [1]）（/）I（&lt;@D1137@&gt; D_1Cs [1]+&lt;@D140@&gt; D_1K [70]）@&gt; D_7其中I表示括号内放射性活度为Bq·kg ~（-1）的源的计算谱中30 ~ 160 keV之间的强度<-1>。通过对腿部体模各种情况下的信噪比进行比较，发现在大骨（直径50 mm）覆盖薄皮（1 mm）的情况下信噪比最佳。4）将本文的计算结果与常规测量结果相结合，提出了一种新的、简单的β发射体在体测量方法。

1) Since 1960's there are a number of experimental works on the external measurement of ^<90>Sr+^<90>Y bremsstrahlung generated by their beta-rays using the whole-body counter installed NaI (Tl) crystal. Quantitative evaluation of the bremsstrahlung yield of ^<90>Sr+^<90>Y has been undertaken using an in-house Monte Carlo code SR90. The optimum organ and the condition for the external measurement of bremsstrahlung using a single detector was investigated under more realistic environment contaminated by the other sources such as ^<137>Cs and ^<40>K.2) Body organs consisted of a large volume bone and also thin skin such as leg, waist and head are considered to be the candidates for the present purpose. As the results of calculations, waist and head were inappropriate because they contain large volume inner soft tissue. Leg phantom approximated by the coaxial cylinder consisted of bone and skin was investigated varying the bone diameter and skin thickness.3) The photon spectrum entering the detector window having 200 mm diameter was obtained. A factor, signal-to-noise ratio s/n, was introduced to judge quantitatively the optimum condition for in-vivo measurements.s/n = <@D7I(<@D190@>D1Sr[1])(/)I(<@D1137@>D1Cs[1]+<@D140@>D1K[70])@>D7in which I means the intensity between 30 and 160 keV in the calculated spectrum for the sources with activities in units of Bq kg^<-1> designated in the bracket. In comparison with s/n ratio for various conditions of leg phantom, the best value was obtained for the case of large bone (50 mm diameter) covered with thin skin (1 mm).4) A possibility of a new and simple method for in-vivo measurement of beta-emitter is suggested by combining the present calculations with the conventional measurements.