Stenting of the Portal Vein Combined with Different Numbers of Iodine-125 Seed Strands: Dosimetric Analyses

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 105 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.