Room: Exhibit Hall
Purpose: To commission the ELEKTA VersaHD linac for Stereotactic Radiosurgery (SRS) treatment using the Agility Multi-Leaf Collimator.
Methods: Ten (n=10) previously treated patients presented with single intracranial metastatic tumors were planned using Monaco. Each plan consisted of 4 dynamic conformal arcs with the goal of providing at least 99% coverage to the PTV, a conformity index (CI) of less than 2.0 (and greater than 1.0) and a dose gradient index (GI) of less than 5.0. Once an acceptable plan was optimized, a verification plan was calculated for Quality Assurance (QA) delivery using the PTW Octavius4D phantom with the PTW 1000SRS detector array. The measurements were compared to the planned data using the PTW Verisoft analysis software. The gamma index was used for the assessment of the comparison using 1% of dose difference and 1 mm distance to agreement. Dose values lower than 30% of the maximum were not considered in the gamma index calculation.
Results: 7 of the 10 plans achieved a PTV coverage of 99%, while the PTV coverage for the remaining plans was compromised due to the proximity of the target to an organ at risk. The average CI was 1.25 and the average GI was calculated 3.37. The QA delivery showed a very good agreement between measured and calculated dose.
Conclusion: All 10 plans suggested that it is indeed feasible for SRS plans to be delivered using a VerdaHD linac. The next step will be to involve patient plans with multiple mets to investigate all aspects of SRS delivery.