Radiotherapy Dose Perturbation of Esophageal Stents Examined in an Experimental Model

Department of Radiation Oncology, Stanford University, Stanford, CA, USA.
International journal of radiation oncology, biology, physics (Impact Factor: 4.26). 04/2011; 82(5):1659-64. DOI: 10.1016/j.ijrobp.2011.02.020
Source: PubMed


To investigate the radiotherapy dose perturbations caused by esophageal stents in patients undergoing external beam treatments for esophageal cancer.
Four esophageal stents were examined (three metallic stents: WallFlex, Ultraflex, and Alveolus; one nonmetallic stent with limited radiopaque markers for visualization: Polyflex). All experiments were performed in a liquid water phantom with a custom acrylic stent holder. Radiochromic film was used to measure the dose distributions adjacent to the stents at locations proximal and distal to the radiation source. The stents were placed in an air-filled cavity to simulate the esophagus. Treatment plans were created and delivered for photon energies of 6 and 15 MV, and data analysis was performed on uniform regions of interest, according to the size and geometric placement of the films, to quantify the dose perturbations.
The three metallic stents produced the largest dose perturbations with distinct patterns of "hot" spots (increased dose) measured proximal to the radiation source (up to 15.4%) and both "cold" (decreased dose) and hot spots measured distal to the radiation source (range, -6.1%-5.8%). The polymeric Polyflex stent produced similar dose perturbations when the radiopaque markers were examined (range, -7.6%-15.4%). However, when the radiopaque markers were excluded from the analysis, the Polyflex stent produced significantly smaller dose perturbations, with maximum hot spots of 7.3% and cold spots of -3.2%.
The dose perturbations caused by esophageal stents during the treatment of esophageal cancer using external beam radiotherapy should be understood. These perturbations will result in hot and cold spots in the esophageal mucosa, with varying magnitudes depending on the stent. The nonmetallic Polyflex stent appears to be the most suitable for patients undergoing radiotherapy, but further studies are necessary to determine the clinical significance of the dose perturbations.

10 Reads
  • [Show abstract] [Hide abstract]
    ABSTRACT: Identify prognostic factors for survival and patterns of treatment failure after definitive radiochemotherapy for esophageal cancer. Between 2003 and 2006, 143 patients with squamous cell carcinoma and adenocarcinoma of the esophagus were retrospectively reviewed. Median age was 65 years (42-81). Median radiation dose was 62.5 Gy (38-72) with 1.8-2 Gy fraction. Median follow-up was 20.8 months (2.8-92.4). Three and 5-year local recurrence-free survival rates were 58.3% and 50.9%. In univariate analysis, traversable esophageal stricture was a prognostic factor. Three, 5-year locoregional recurrence-free survival rates were 42.4% and 34.9%. In multivariate analysis, traversable esophageal stricture and stage < IIB were independent prognostic factors. Three and 5-year disease-free survival rates were 30.5% and 25.9%. In multivariate analysis, Nutritional Risk Index (NRI) ≥ 97.5 and performance status (PS) = 0 were independent prognostic factors. Median, 3, and 5-year overall survival rates were 22.1 months, 34.4%, and 19.8%. In multivariate analysis, independent prognostic factors were NRI ≥ 97.5 and PS = 0. Median survival times for the NRI classes (no denutrition, moderate and severe denutrition) were 29.5, 19.7, and 12 months (P = 0.0004), respectively. A major impact of baseline NRI was found in terms of survival; it should be included in future prospective trials.
    No preview · Article · Oct 2012 · Diseases of the Esophagus
  • [Show abstract] [Hide abstract]
    ABSTRACT: Background: Self-expandable esophageal stents are increasingly used for palliation or as an adjunct to chemoradiation for esophageal neoplasia. The optimal esophageal stent design and material to minimize dose perturbation with external beam radiation are unknown. We sought to quantify the deviation from intended radiation dose as a function of stent material and mesh density design. Methods: A laboratory dosimetric film model was used to quantify perturbation of intended radiation dose among 16 different esophageal stents with varying material and stent mesh density design. Results: Radiation dose enhancement due to stent backscatter ranged from 0 % to 7.3 %, collectively representing a standard difference from the intended mean radiation dose of 1.9 (95 % confidence interval [CI] 1.5 - 2.2). This enhancement was negligible for polymer-based stents and approached 0 % for the biodegradable stents. In contrast, all metal alloy stents had significant radiation backscatter; this was largely determined by the density of mesh design and not by the type of alloy used. Conclusions: Stent characteristics should be considered when selecting the optimal stent for treatment and palliation of malignant esophageal strictures, especially when adjuvant or neo-adjuvant radiotherapy is planned.
    No preview · Article · Jan 2013 · Endoscopy
  • [Show abstract] [Hide abstract]
    ABSTRACT: It is the purpose of this study to evaluate how self-expanding stents (SESs) affect esophageal cancer radiation planning target volumes (PTVs) and dose delivered to surrounding organs at risk (OARs). Ten patients were evaluated, for whom a SES was placed before radiation. A computed tomography (CT) scan obtained before stent placement was fused to the post-stent CT simulation scan. Three methods were used to represent pre-stent PTVs: 1) image fusion (IF), 2) volume approximation (VA), and 3) diameter approximation (DA). PTVs and OARs were contoured per RTOG 1010 protocol using Eclipse Treatment Planning software. Post-stent dosimetry for each patient was compared to approximated pre-stent dosimetry. For each of the three pre-stent approximations (IF, VA, and DA), the mean lung and liver doses and the estimated percentages of lung volumes receiving 5 Gy, 10 Gy, 20 Gy, and 30 Gy, and heart volumes receiving 40 Gy were significantly lower (p-values < 0.02) than those estimated in the post-stent treatment plans. The lung V5, lung V10, and heart V40 constraints were achieved more often using our pre-stent approximations. Esophageal SES placement increases the dose delivered to the lungs, heart, and liver. This may have clinical importance, especially when the dose-volume constraints are near the recommended thresholds, as was the case for lung V5, lung V10, and heart V40. While stents have established benefits for treating patients with significant dysphagia, physicians considering stent placement and radiation therapy must realize the effects stents can have on the dosimetry.
    No preview · Article · Jul 2013 · Journal of Applied Clinical Medical Physics
Show more