In vitro Dosimetric Study of Biliary Stent Loaded with Radioactive 125I Seeds

Abstract

Background:A novel radioactive 125I seed-loaded biliary stent has been used for patients with malignant biliary obstruction. However, the dosimetric characteristics of the stents remain unclear. Therefore, we aimed to describe the dosimetry of the stents of different lengths — with different number as well as activities of 125I seeds.Methods:The radiation dosimetry of three representative radioactive stent models was evaluated using a treatment planning system (TPS), thermoluminescent dosimeter (TLD) measurements, and Monte Carlo (MC) simulations. In the process of TPS calculation and TLD measurement, two different water-equivalent phantoms were designed to obtain cumulative radial dose distribution. Calibration procedures using TLD in the designed phantom were also conducted. MC simulations were performed using the Monte Carlo N-Particle eXtended version 2.5 general purpose code to calculate the radioactive stent's three-dimensional dose rate distribution in liquid water. Analysis of covariance was used to examine the factors influencing radial dose distribution of the radioactive stent.Results:The maximum reduction in cumulative radial dose was 26% when the seed activity changed from 0.5 mCi to 0.4 mCi for the same length of radioactive stents. The TLD's dose response in the range of 0–10 mGy irradiation by 137Cs γ-ray was linear: y = 182225x − 6651.9 (R2= 0.99152; y is the irradiation dose in mGy, x is the TLDs’ reading in nC). When TLDs were irradiated by different energy radiation sources to a dose of 1 mGy, reading of TLDs was different. Doses at a distance of 0.1 cm from the three stents’ surface simulated by MC were 79, 93, and 97 Gy.Conclusions:TPS calculation, TLD measurement, and MC simulation were performed and were found to be in good agreement. Although the whole experiment was conducted in water-equivalent phantom, data in our evaluation may provide a theoretical basis for dosimetry for the clinical application.

Technical note: A fast and accurate analytical dose calculation algorithm for 125I seed‐loaded stent applications

“…Using the same setup of prescription points and the same ROI defined in Jung et al, 16 (ROI ref ), our study showed a larger decrease of the doses at the prescription points (17.8% vs. 10.8%-14.8%) and a larger deviation of the radial doses on the surface of ROI ref (10.8% vs. 4.3%). Compared with Yao et al, 19 the influence of the stent on the radial dose rate is much larger in our work (24.2% vs. 6.9%) for the 6-cm stents loaded with 16 125 I seeds. These differences are mainly caused by the different stent geometries adopted.…”

“…Yao et al evaluated the dosimetry of seed-loaded stent models of three configurations using Monte Carlo (MC) simulations, TG-43 methods implemented in a TPS, and thermoluminescent dosimeter (TLD) measurements, and their results suggested that the influence of the metal stent on the dose distribution was negligible. 19 Jung et al investigated the dose distributions surrounding 125 I seed-loaded stents with a diameter of 12 mm and a length of 60 mm by MC simulation and they found that the impact of metallic stent was significant. 16 Considering the disagreement in the conclusions of these previous studies, it was deemed necessary to further study the dose influence of stent, especially when the previous studies adopted simplified stent models.…”

“…Yao et al. evaluated the dosimetry of seed‐loaded stent models of three configurations using Monte Carlo (MC) simulations, TG‐43 methods implemented in a TPS, and thermoluminescent dosimeter (TLD) measurements, and their results suggested that the influence of the metal stent on the dose distribution was negligible 19 . Jung et al.…”

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

“…With increasingly detailed studies of intraluminal implantation of 125 I seed-loaded stents,[ 23 ] stenting of the portal vein combined with implantation of 125 I seed strands has become a new treatment of HCC with PVTT. In clinical application of this technology, most researchers have used the formula: obstruction length (mm)/4.5 + 4 to calculate the required number of 125 I seeds.…”

Brachytherapy Drainage Catheter and Chemotherapy for Unresectable Pancreatic Carcinoma Combined with Obstructive Jaundice

“…A suitable alternative is the use of 125 I radioactive seeds that can continuously release low-dose grays to inhibit cancer cells and promote apoptosis. Many animal and clinical studies have confirmed that 125 I brachytherapy can obviously increase the local control rate and improve long-term survival (10)(11)(12)(13). At present, the most commonly tools for the permanent implantation of radioactive 125 I seeds is CT or US guidance, which requires percutaneous trans-stomach puncture to the tumor located at the head of pancreas frequently, which is a high-risk treatment due to the complex surrounding vessels.…”