γ射线外照射条件下体模红骨髓剂量及剂量深度分布的蒙特卡罗计算

CALCULATION OF RED BONE MARROW DOSE AND DOSE DEPTH DISTRIBUTION IN PHANTOM FROM EXTERNAL GAMMA RADIATION

用蒙特卡罗方法,对0.025、0.05、0.11、0.30、0.661、1.25、3.0和6.OMeV等八种能量的平行宽束γ射线沿垂直于体模中心轴线方向的旋转照射,位于体模躯干下端离体模中心轴线的距离分别为50、100和200cm的1.25MeVγ点源对体模正面照射,1.25MeV平行宽束γ射线对体模正面、背面和侧面方向的垂直照射,以及当体模处于年龄为22.5小时的落下灰γ辐射场中时,计算了体模的红骨髓平均剂量D_m、干细胞活存率计权等效剂量D_(sw)和组织吸收剂量的深度分布。计算结果,除低能(<0.05MeV)γ射线和近距离(距体模中心2m以内)点源照射条件之外,D_m和D_(sw)在2％以内相符。对于在落下灰γ辐射场中测量人体红骨髓平均剂量的仪器,可用1.25MeVγ射线平行宽束旋转照射条件进行刻度。

Calculations with the Monte-Carlo method were performedfor red bone marrow dose,equivalent dose weighted by the stem cel1survival rate and dose depth distribution in the phantom, Which wassupposed to be exposed to three different gamma radiation fields: a broadparalled one with energies between 0.025 and 6.0 MeV, under the conditionof rotated exposure,the aligned and expanded one with energy of 1.25MeV, and a fallout gamma radiation field.As a result,except for lowenergy (lower than 0.05 MeV) and a point source radiations at shortdistance (less than 2 m from phantom center),the mean red marrow doseis in agreement with the equivalent dose weighted by stem cell survivalrate within 2%. The results suggest that the gamma dose monitoringinstrument used in the fallout radiation field,may successfully becalibrated with the broad parallel gamma radiation of 1.25MeV under thecondition of rotated exposure.