Single Fraction Stereotactic Body Radiation Therapy (SBRT) for Spine Metastasis: A Dosimetric Comparison of Multiple Treatment Delivery Systems

98.9%. The mismatch became more pronounced with smaller field size. The Gamma passing rate decreased to 38% from 52% when the DMLC field size changed from 5 x 5 cm to 3 x 3 cm. These gantry/collimator rotation induced discrepancies in DMLC delivery could be significantly reduced if additional angular dependent “shift” (averaged w1.7 mm, a resultant of 2D shifts) was applied to the dose distribution. When this was done, the Gamma passing rate increased to 93% from 56%. The value of these “shifts” was independent of field size. Overall, there were no observed differences in Gamma passing rates using different dose rates or different prescribed dose gradients. Conclusions: We found that smaller DMLC fields have larger variations in dose distribution from collimator rotations. The passing rate improved by applying a set of constant shifts. However, the clinical significance of these variations needs to be further evaluated. Author Disclosure: J. Li: None. C. Burman: None. K. Schupak: None. M. Chan: None.