SU-GG-T-540: Intensity-Modulated Arc Therapy for Stereotactic Radiotherapy of Spinal & Paraspinal Tumors

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Purpose: Stereotactic radiosurgery of metastatic spinal tumor with intensity‐modulated radiotherapy(IMRT) technique requires a long treatment time due to an extensive monitor units (MU) resulting from multiple highly intensity‐modulated beams in order to sparing adjacent spinal cord and other critical structures. This study investigates the feasibility of using intensitymodulated arc therapy (IMAT) as an alternative modality with a shorter treatment time while maintaining a compatible dosimetric performance as IMRT technique. Methods/Materials: 8 patients with spinal or paraspinal tumor were recruited in this study. All those patients were previously treated with IMRT technique, in which 18Gy or 24Gy doses were delivered in a single fraction with 11 to 13 coplanar radiation beams. Single arc and 2‐arc IMAT plans were retrospectively generated for each patients using RapidArcTM treatment planning system (Varian Medical System, Sunnyvale, CA). The previous delivered IMRT plans were chosen as a reference. The differences of following parameters between IMAT and IMRT plans were used to evaluate the plan performance: the volumes of PTV receiving 95% and 100% of prescribed dose(V95, V100), the maximum spinal cord dose (MSPDOSE) and the total monitor units (TMU). Results: For all 8 patients, the differences of V95 and V100 between single arc IMAT and IMRT plans are −5.3%±4.8% and −9.3%±7.8% , while the difference of MSPDOSE is 0.23Gy±0.87Gy. In contrary, the differences of V95 and V100 between 2‐arc IMAT and IMRT plans are −0.67%±2.01%, −1.1%±2.23% , while the difference of MSPDOSE is 0.38Gy±0.47GY. The ratios of TMU of single arc and 2‐arc IMAT plans over IMRT plan are 55%±19% and 65%±17%. Conclusion: For stereotactic radiosurgery of spinal tumor,IMRT plan provide better dose coverage than single arc IMAT plan, but 2‐arc IMAT plan is capable of providing a compatible dosimetric performance as IMRT plan while significantly reducing the treatment time.