title: Radiotherapy dose perturbation of metallic esophageal stents.
abstract: OBJECTIVE
  Metallic esophageal stents frequently present during the treatment of esophageal cancer while using either external beam radiotherapy or brachytherapy. The dosimetric effects due to these metallic stents have not been reported. This work investigates these dose effects for various stent models presented during a radiotherapy procedure.
  
  
  METHODS
  Two types of representative stent models, shell and ring stents, with various designs (e.g., composition and shell thickness or ring spacing), were studied. Three Monte Carlo code systems (EGS4/BEAM, EGSnrc/DOSRZnrc, and MCNP) were used to calculate the dose distributions for 6- and 15-MV external photon beams and for a (192)Ir brachytherapy source with and without a metallic esophageal stent in place.
  
  
  RESULTS
  For a single external beam, a dose enhancement is generally observed in front of the stent (upstream) in the region within 4-mm distance of the stent surface. The enhancement at 0.5-mm distance from the stent surface can be as high as 20%. The dose behind the stent (downstream) is generally reduced. For a parallel-opposed pair (POP), a dose enhancement is always observed in the region within 3-mm distance of the stent surface. The enhancement at 0.5-mm distance from the stent surface can be as high as 10% for the 15-MV POP and 8% for the 6-MV POP. The dose effects depend on stent design (e.g., composition, thickness of shell stent, or ring spacing in ring stents). This dependence is reduced for a POP. In the case of the (192)Ir brachytherapy source, a dose enhancement is observed in the region within 1-mm distance from the stent surface. The dose enhancement is approximately 5% at 0.5-mm distance from the stent surface.
  
  
  CONCLUSIONS
  The dose perturbations due to the presence of a metallic esophageal stent during the treatment of esophageal cancer while using either external beam radiotherapy or brachytherapy should be recognized. These perturbations result in an overdose in esophageal mucosa. The overdose is within 5%-10% at a depth of 0.5 mm in the esophageal wall.
authors.affiliation: Department of Radiation Oncology, University of Maryland, 22 South Greene Street, Baltimore, MD 21201-1595, USA. ali001@umaryland.edu
authors.forename: X Allen
authors.initials: XA
authors.lastname: Li
authors.forename: Omar
authors.initials: O
authors.lastname: Chibani
authors.forename: Bruce
authors.initials: B
authors.lastname: Greenwald
authors.forename: Mohan
authors.initials: M
authors.lastname: Suntharalingam
mesh_terms: D001918:Brachytherapy; D004938:Esophageal Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008670:Metals; D009010:Monte Carlo Method; D011879:Radiotherapy Dosage; D015607:Stents
chemical_list: D008670:Metals