Effect of stents on radiation dosimetry for esophageal cancer.

Abstract

48 Background: To evaluate how self-expanding metal stents (SEMS) affect esophageal cancer radiation planning target volumes (PTVs) and dose delivered to surrounding organs-at-risk (OARs). Methods: Ten patients were evaluated for whom a SEMS was placed before radiation. A 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) - PTVs were contoured based on the pre-stent CT, 2) Volume Approximation (VA) - the post-stent PTV was altered to approximate the pre-stent PTV based on differences in esophageal volumes between scans, and 3) Diameter Approximation (DA) - the post-stent PTV was altered based on differences in esophageal diameters. 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. Results: For the IF, VA, and DA methods, the post-stent PTVs were larger than pre-stent PTVs by an average of 155, 68, and 67 cm3, respectively. Pre-stent heart and lung doses were less than post-stent using VA and DA; however, IF only yielded a significantly lower heart V40 (Table). Liver, spinal cord, and kidney doses were not significantly different between planning methods. Conclusions: Placement of an esophageal SEMS increased the PTV size for radiation planning, causing a statistically significant increase in heart and lung radiation doses, although the absolute dose increase was relatively small. Most patients receiving stents will have no increased risk of radiation-induced toxicity. In patients where one anticipates difficulty meeting crucial dose constraints, it may be preferable to consider avoidance of stenting before radiotherapy. [Table: see text]