Respiratory-driven lung tumor motion is independent of tumor size, tumor location, and pulmonary function

Purpose: To determine whether superior-inferior lung tumor motion is predictable by tumor size or location, or pulmonary function test results. Methods and Materials: Superior-inferior tumor motion was measured on orthogonal radiographs taken during simulation of 22 patients with inoperable lung cancer diagnosed by orthogonal radiographs. Results: The tumor size averaged 5.5 ± 3.1 cm (range 1.5-12 cm). Seven of 11 central tumors demonstrated some motion compared with 5 of 11 peripheral tumors. Four of 5 upper lobe tumors moved compared with 8 of 17 tumors that were either middle or lower lobe lesions. The mean fourth rib motion was 7.3 ± 3.2 mm (range 2-15). The mean FeV₁ was 1.8 ± 1.2 (range 0.55-5.33. The mean diffusing capacity of the lung for carbon monoxide was 14.0 ± 6.5 (range 7.8-21.9). The mean total lung capacity was 6.5 ± 1.2 (range 3.3-8.4). None of these parameters correlated with tumor motion. Although lateral tumor motion could not be consistently determined, 1 tumor moved 10 mm anterior-posteriorly. Conclusions: Lung tumors often move significantly during respiration. Tumor motion is not predictable by tumor size or location, or pulmonary function test results. Therefore, tumor motion must be measured in all patients. Measurement in three dimensions will likely be necessary to maximize the irradiated lung volumes or choose beam arrangements parallel to the major axis of motion.