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Effect of stents on radiation dosimetry for esophageal cancer.

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].