Robustness of single-isocenter multiple-metastasis stereotactic radiosurgery end-to-end testing across institutions

Abstract Background The accuracy of stereotactic radiosurgery to multiple brain metastases with a single isocenter using high definition dynamic radiosurgery (HDRS) was evaluated to assess robustness, repeatability, and possibility of inter-institutional quality assurance amongst multiple institutions. Methods A CT simulation scan obtained from a previously treated patient was used as the data set for targeting seven brain lesions. A VMAT treatment plan was generated using Monaco and was replicated at six HDRS-capable institutions using a plan template. All institutions subsequently irradiated 3D-printed head anthropomorphic phantoms mimicking the patient’s anatomy. Three different phantoms with a point dosimeter insert, film insert, and a gel dosimeter were used. Absolute dosimetry end-to-end dosimetric accuracy as well as gamma analysis for relative dose distribution agreement analysis was used to evaluate measurement agreement with calculation. Results Point measurements averaged across all institutions using six-degree-of-freedom treatment positioning correction were within 1.2±0.5%. The average gamma passing rate in the film plane using 3D global 3D gamma analysis was 96.6±2.2% (3%/2 mm). For all targets within 4 cm of the isocenter, the 3D dosimetric gel gamma passing rate averaged across institutions was >90% (3%/2 mm). 88.0% average gamma passing rate was found for targets beyond 4 cm. The targeting accuracy of high definition dynamic radiosurgery assessed by geometrical offset of the center of dose distributions was established across multiple institutions in this study to be within 1 mm for targets within 4 cm of isocenter. Conclusions Across variations in clinical practice, comparable dosimetry and localization is possible with this treatment planning and delivery technique.