A study for the dosimetric evaluation of rotational setup error for lung stereotactic body radiation therapy (vol 78, pg 561, 2020)

Purpose: To investigate the necessity of rotational shifts by considering dosimetric impact of rotational errors on stereotactic body radiation therapy (SBRT). Materials and methods: 20 lung patients with the lesion size <5 cm treated with SBRT have been selected for dosimetric analysis. Three-dimensional dose has been rotationally shifted (+/- 1 degrees, +/- 3 degrees, +/- 5 degrees for pitch, roll and yaw) and overlaid to the original computed tomography images. The dose-volume histograms of 18-rotational plans of each patient were compared to those of the original plan. Results: No significant dosimetric differences were observed in target coverage. For all of the cases up to 5 degrees in any couch angle dose differences of D-99 and D-95 were <3%. Variations of conformity index were observed to be less than 0.05. None of the organ at risk doses exceeded the dose limit. The V-20 differences of the ipsilateral and the total lungs were less than 0.4%. Conclusion: It has been found to be unnecessary to perform rotational shifts up to 5 degrees for lung SBRT treatments; the translational shift is sufficient for the cases used in this study. This method may be applied and tested after planning and before treatment initiation to rule out exceptionally extreme cases.