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 (I) 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 I 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 I seed strands (Groups I, II, and III, respectively). At different prescribed doses (PDs), I 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 I seed activity, when the I seed strand increased from one chain to two, D (dose delivered to 90% of the target volume) increased by ≥184%; when it increased from two chains to three, D increased by ≥63%. When the PD was 105 Gy and I seed strands increased from one chain to two, V (percentage of the target volume receiving ≥90% of the PD) increased by 158-249%; when it increased from two chains to three, V increased by 7-175%. CN was correlated positively with I seed activity (B = 0.479, P < 0.001) and number of I 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 I seed strand could not meet dosimetry requirements. For a stent combined with two I 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 I 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.