Esophageal cancer patients undergoing external beam radiation after placement of self-expandable metal stents: is there a risk of radiation dose enhancement?

摘要

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. DESIGN: Simulated clinical protocol. SETTING: Linear accelerator radiation treatment center. PATIENTS: 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. INTERVENTIONS: Radiation beams composed of photons (x-rays) delivered in split dosing with energies of 6, 10, and 15 million volts. MAIN OUTCOME MEASUREMENTS: 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. LIMITATIONS: 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.