Room: ePoster Forums
Purpose: This study was to investigate the effect of the rotational error on the dose distribution with single-isocenter technique of stereotactic radiotherapy for multiple brain metastases.
Methods: The two simulated spherical targets with a diameter of 2 cm, which were arranged with three coordinates, were used in this study. The center coordinate (unit: cm) of each target was arranged under the following three conditions: (a) (10, 0, 0), (-10, 0, 0), (b) (10, 10 ,0), (-10, -10, 0), and (c) (10, 10, 10), (-10, -10, -10) for the isocenter which was set as the origin of the coordinate axes. The dose distributions were created so that each target was entirely covered by 100% of the prescribed dose. After that, the position vectors of the dose distributions were rotated by quaternion within a range of 0 to 2.0 degrees (in 0.5 degrees increments) around the roll, pitch, and yaw axes. The dose coverages of the targets at each rotation angle were calculated and compared with case at 0 degrees.
Results: The dose coverages in condition (a) were 99.8%, 94.6%, and 94.2% for 1.0 degree, 99.5%, 89.8%, and 89.0% for 2.0 degrees for roll, pitch, yaw, respectively. Those in condition (b) were 94.2%, 92.9%, and 94.2% for 1.0 degree, 89.0%, 86.7%, and 89.0% for 2.0 degrees, respectively. In condition (c), the coverages were 92.2%, 92.9%, and 92.2% for 1.0 degree, 85.6%, 86.7%, and 85.6% for 2.0 degrees, respectively. The coverages for targets were decreased as the rotational error and the distance from the isocenter was increased.
Conclusion: Our early results suggest that the rotational error has a great influence on the dose distribution when the distance between the targets and the isocenter is large. We should pay close attention to the rotational error in stereotactic radiotherapy for the multiple brain metastases.