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Impact of Air in the Esophagus During Proton Radiation Therapy

C Bloch1*, B Nguyen2 , S Apisarnthanarax1 , J Zeng1 , T Wong2 , (1) University of Washington School of Medicine, Seattle, WA, (2) SCCA Proton Therapy Center, Seattle, WA


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: to evaluate the dosimetric impact of air in the esophagus on proton therapy treatment plans for patients with esophageal cancer.

Methods: 10 patients were treated with proton therapy for esophageal cancer. All patients were treated with scanned pencil beam delivery including at least 2 fields to reduce the impact of motion interplay effects. Treatment plans are generated based on CT scans which may have air in the esophagus. Margins were typically at least 5 mm from iGTV to CTV and another 5mm from CTV to PTV, but sometimes custom margins were larger. Additional CT scans were performed during the course of treatment to evaluate the dosimetric impact of anatomical changes including resolution of air pockets or additional air pockets.

Results: Air pockets in the esophagus can impact the range of protons. Overriding the air as tissue density results in significant dosimetric differences, which are not accurate. In most patients air pockets in the esophagus were consistent with subsequent CT scans. In cases where the air pockets resolved, the esophageal wall closes up. The density of esophagus tissue in the beam path resulting from air or no air will be similar even when the shape changes. Therefore we determined that not overriding the air inside the esophagus provides the most consistent results and avoids potentially over-ranging into normal tissue.

Conclusion: Air pockets in the esophagus are generally consistent and do not lead to significant dosimetric changes. It is recommended that plans be optimized without overriding the air density Periodic volumetric imaging throughout the course of treatment should be used to evaluate the treatment and potentially adapt the treatment plan if significant changes are noted.


Not Applicable / None Entered.


TH- External Beam- Particle therapy: Proton therapy - treatment planning/virtual clinical studies

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