Assessment of dose distribution in pancreatic SABR in the presence of a metallic biliary stent using Monte Carlo modeling
Abstract
Background: Stereotactic ablative radiotherapy (SABR) with dose escalation is increasingly used for pancreatic cancer; however, the dosimetric impact of metallic biliary stents remains poorly characterized. Self-expanding metal stents (SEMS), commonly placed for obstructive jaundice, contain high-density nitinol that produces computed tomography (CT) artifacts, including beam hardening, potentially compromising treatment planning system (TPS) dose accuracy. Precise dose estimation is critical given the proximity of the duodenum and other organs at risk (OARs).
Purpose: This study evaluated dose distribution in pancreatic SABR in the presence of a metallic biliary stent using Monte Carlo (MC) simulation with refined stent contouring and material correction.
Methods: Two patients with SEMS (Cook Evolution, nitinol alloy) treated with SABR (50 Gy in 5 fractions) using volumetric modulated arc therapy (VMAT) were retrospectively analyzed. Plans were generated in Eclipse TPS (v.13.7) using the analytical anisotropic algorithm. MC simulations were performed in PRIMO (PENELOPE-based) with ≤2% uncertainty. A novel contouring technique separated the hollow lumen from the metallic stent wall to correct CT beam hardening artifacts. Nitinol (density 6.45 g/cm3) was incorporated into MC calibration. Comparisons between standard MC, modified MC, and TPS were assessed using percentage agreement (PA), gamma passing rate (GPR; 3%/3 mm), and dose-volume histogram metrics.
Results: Refined…
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