CT analysis of mucosal surface dose in intraluminal irradiation for esophageal cancer

PURPOSE: Balloon applicators are generally used in intraluminal irradiation for esophageal cancer. CT exhibits a distortion of the applicator during treatment. Because little attention has been paid to dose non-uniformity in the esophageal mucosa, we analyzed mucosal surface dose using CT. MATERIALS AND METHODS: Eleven patients with esophageal cancer treated with a double-lumen balloon applicator (balloon length: 15 cm, diameter: 20 mm) were evaluated. Reference dose was prescribed at 5 mm under the mucosal surface. Mucosal surface points were determined from CT images, and relative surface dose to reference dose was calculated. Hot and cold spots were defined respectively, as dose points receiving at least 200% and less than 100% of the reference dose. RESULTS: The mean mucosal dose ranged from 138% to 174%. Mucosal dose was distributed widely from 100% to 199% in 94% of all patients. Hot and cold spots accounted for 5.3% and 0.7% of mucosal dose points, respectively. CONCLUSION: 1) CT analysis exhibited the inhomogeneity of esophageal mucosal dose in intraluminal irradiation. 2) At present, it is acceptable to prescribe the reference dose at 5 mm under the esophageal surface. 3) Balloon applicators should be improved to achieve dose uniformity in the esophageal mucosa.