SU-F-T-297: Quality Assurance of Multiple Brain Metastases with Single Isocenter Using Measurement Guided Dose Reconstruction

Authors


Abstract

Purpose:

To evaluate the use of measurement guided dose reconstruction (MGDR) in quality assurance (QA) of stereotactic radiosurgery (SRS) of multiple brain metastases (MBM) planned with single isocenter (SI).

Methods:

Seven clinically approved multi-isocenter MBM (MI-MBM) plans were re-optimized using SI (SI-MBM) by coplanar volumetric arc therapy (VMAT) in Monaco v5.0 (Elekta CMS, Maryland Heights, MO, USA). These plans were delivered on an Elekta Agiltiy Linac and measured by OCTAVIUS 4D system with OCTAVIUS 1500 2D array (PTW, Freiburg, Germany). Measurements were repeated with a shift of the phantom by 5mm to double the detector resolution. 3D γ analysis in Verisoft 6.1 with 1.5mm/1.5%, 1.5mm/2% and 2mm/2% at local-dose passing criteria and 20% dose suppression were made.

Results:

3D γ passing rates are 94.3±2.7%, 85.2±5.4% and 84±5.7% at 1.5mm/1.5%, 1.5mm/2% and 2mm/2% criteria.

Conclusion:

MGDR of OCTAVIUS 4D system provides adequate and efficient VMAT QA solution for SI-MBM SRS. However, the results showed significant spatial dependence due to rapid dose fall-off in radiosurgery. Further improvement in detector spatial resolution is desired. PTV margins should be carefully adopted for those MBM treated with single isocenter.

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