Background and purpose: To evaluate intrafractional gastric motion and interfractional variability of the stomach shape during radiation therapy (RT) for gastric lymphoma. Materials and methods: For 11 patients with gastric lymphomas, we undertook fluoroscopic examinations at the time of the simulation, and once a week during RT to evaluate inter- and intrafractional gastric variations. We recorded anteroposterior and left to right X-ray images at inhale and exhale in each examination. We gave coordinates based on the bony landmarks in each patient, and identified the most superior, inferior, lateral, ventral, and dorsal points of the stomach on each film. The interfractional motion was assessed as the distance between a point at inhale and the corresponding point at exhale. We also analyzed interfractional variation based on each point measured. Results: The intrafractional gastric motion was 11.7 ± 8.3, 11.0 ± 7.1, 6.5 ± 6.5, 3.4 ± 2.3, 7.1 ± 8.2, 6.6 ± 5.8 mm (mean ± SD) for the superior, inferior, right, left, ventral and dorsal points, respectively, which was significantly different between each point. The interfractional variability of stomach filling was -2.9 ± 14.4, -6.0 ± 13.4, 9.3 ± 22.0 mm for the superior-inferior (SI), lateral (LAT), and ventro-dorsal (VD) directions, respectively, and the differences of variabilities were also statistically significant. Thus, the appropriate treatment margins calculated from both systematic and random errors are 30.3, 41.0, and 50.8 mm for the SI, LAT, and ventro-dorsal directions, respectively. Conclusions: Both intrafractional gastric motion and interfractional variability of the stomach shape were considerable during RT. We recommend regular verification of gastric movement and shape before and during RT to individualize treatment volume.
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