Abstract： Background:Portal-vein stent combined with one iodine-125 (125I) seed strand has become a new treatment for portal vein tumor thrombosis.However,dosimetric aspects of this irradiation stent have not been reported.Therefore,we aimed to undertake dosimetric analyses comparing portal-vein stents combined with different numbers of 125I seed strands.Methods:A water cylinder was created by a treatment-planning system to simulate a portal-vein stent.The stent was combined with one,two,or three 125I seed strands (Groups Ⅰ,Ⅱ,and Ⅲ,respectively).At different prescribed doses (PDs),125I seeds of identical activities were loaded on Groups Ⅰ-Ⅲ.Conformation number (CN),external volume index,and homogeneity index were calculated.Linear regression analyses were used to evaluate the obtained data.Results:For identical 125I seed activity,when the 125I seed strand increased from one chain to two,D90 (dose delivered to 90％ of the target volume) increased by ≥184％;when it increased from two chains to three,D90 increased by ≥63％.When the PD was 105 Gy and 125I seed strands increased from one chain to two,V100 (percentage of the target volume receiving ≥90％ of the PD) increased by 158-249％;when it increased from two chains to three,V100 increased by 7-175％.CN was correlated positively with 125I seed activity (B =0.479,P ＜ 0.001) and number of 125I seed strands (B =0.201,P ＜ 0.001) and was independent of PD (B =-0.002,P =0.078).Conclusions:A portal-vein stent combined with a single 125I seed strand could not meet dosimetry requirements.For a stent combined with two 125I seed strands,when the PD was 1 05 Gy and seed activity was 0.7 mCi,the dose distribution could satisfy dosimetry requirements.For a stent combined with three 125I seed strands,if the PD was 105,125,or 145 Gy,the recommended seed activities were 0.5,0.5,and 0.6 mCi,respectively.