title: Esophageal cancer patients undergoing external beam radiation after placement of self-expandable metal stents: is there a risk of radiation dose enhancement?
abstract: BACKGROUND
  Self-expandable metal stents (SEMSs) are used for palliation of malignant dysphagia. It is not known whether dose adjustments are required when there is a stent in the radiation field.
  
  
  OBJECTIVE
  To measure the effects of esophageal stents of various designs and materials on radiation dose to the tissue adjacent to the stent in the radiation field to determine whether there should be any dose adjustment.
  
  
  METHODS
  Simulated clinical protocol.
  
  
  METHODS
  Linear accelerator radiation treatment center.
  
  
  METHODS
  Solid Water phantoms were used to mimic the tissue environment of the human esophagus as well as stents of various designs and materials and controls.
  
  
  METHODS
  Radiation beams composed of photons (x-rays) delivered in split dosing with energies of 6, 10, and 15 million volts.
  
  
  METHODS
  Film and image-based evidence of dose enhancement; Monte Carlo calculations.
  
  
  RESULTS
  Dose enhancement from single beams was seen only on the anterior surface, particularly in the stainless steel Z-stent (3.5%-7.8%) and the nonmetal Polyflex stent (5.5%-8.8%); less dose enhancement was seen on the anterior surface of the Alimaxx and Ultraflex nitinol stents (2%-2.5%). A negligible dose effect was seen on the posterior wall of all the stents tested. Monte Carlo calculation results were roughly similar to actual dosimeter measurements.
  
  
  CONCLUSIONS
  Simulated clinical protocol.
  
  
  CONCLUSIONS
  This tissue-mimicking model reveals that radiation dose enhancement is a function of stent design and material, and the dose reduction is unnecessary as long as multiple fields are used.
authors.affiliation: Division of Gastroenterology and Hepatology, University of Colorado Denver, Aurora, Colorado 80045-2541, USA.
authors.forename: Yang K
authors.initials: YK
authors.lastname: Chen
authors.forename: Tracey E
authors.initials: TE
authors.lastname: Schefter
authors.forename: Francis
authors.initials: F
authors.lastname: Newman
mesh_terms: D001672:Biocompatible Materials; D003680:Deglutition Disorders / Q000628:therapy*; D004867:Equipment Design; D004938:Esophageal Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008422:Materials Testing; D008670:Metals; D009010:Monte Carlo Method; D010166:Palliative Care; D011874:Radiometry; D011879:Radiotherapy Dosage; D015607:Stents / Q000009:adverse effects*
chemical_list: D001672:Biocompatible Materials; D008670:Metals