LAUSR

Purpose To establish a suitable routine for handling of internal patient motions during radiotherapy delivery it is valuable to have information on the actual motions in a large group of patients. This presentation focus on a study (Sarudis et al., Acta Oncologica 2016; 56) that provides information on the lung-tumor motions due to breathing for 126 patients treated with stereotactic body radiotherapy. Methods Four-dimensional computed tomography images were reviewed. The tumor motion was determined by the center-of-mass shift between the breathing phases containing the largest positional differences. Patients were evaluated separately in subgroups depending on tumor diameter (O   5.0 cm) and location within the lung (upper, middle, lower lobe). The motion pattern in each direction (interior-superior, left-right, and anterior-posterior) were analyzed for tumors moving >5 mm and sinusoidal trigonometric functions were fitted using the least mean square method. Mann-Whitney statistical tests were used for statistical analyses. Results Tumor volumes were between 1.6 and 52.3 cm3. The mean and maximum amplitudes of the tumor motions were 6.9 and 53.0 mm (inferior-superior), 1.5 and 11.0 mm (left-right), and 2.5 and 9.0 mm (anterior-posterior). 95% of the tumors moved ≤20 mm, ≤3 mm, and ≤6 mm in the inferior-superior, left-right and anterior-posterior directions respectively. The observed motions showed no correlation with tumor size or location except for motions in the inferior-superior direction where the motion amplitude significantly increased for tumors located in the middle compared to the upper as well as in the lower compared to the middle part of the lung. The motion pattern of a tumor was always best described using a squared trigonometric function: A · sin 2 t π T - B , where A = maximum amplitude, t = time of measurement, T = total time of the breathing cycle and B is a constant used to synchronize the starting point of the breathing cycle. Conclusions Lung-tumor movements were most pronounced in inferior-superior direction and the motion amplitude in this direction was larger for tumors located in the lower compared to the upper part of the lung. Tumor size did not correlate with motion amplitude. The motion pattern was in all cases best described with a squared sinusoidal function.