(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: technique of treating multiple brain metastases with a single isocenter has been gaining popularity in recent years. In this study, we investigated the feasibility of the Brainlab Elements Multiple Brain Mets SRS together with our Novalis TX Linac for this application.
Methods: patients with a total of fifty-six brain tumors were selected for this study. The number of tumors per patient ranged from 6 to 18. To limit the positioning error due to Linac angular uncertainty, the distance from the isocenter to each tumor in a plan was constrained to no more than 5 cm. Each of the five cases took two plans to complete the treatment. The completed plans were exported to Varian Eclipse. The dose distribution was re-calculated with the AAA algorithm in Eclipse for the purpose of secondary monitor unit check. The criterion for comparison between Elements Monte Carlo and Eclipse AAA was the mean dose to the PTVs. The plans were also delivered to a Sun Nuclear MapCheck 2 device inserted into a home-made solid water phantom on our Novalis Tx linear accelerator. Every conformal arc was shot at its actual couch angle to detect the potential error of couch movement. Each plan might be shot multiple times with Mapcheck at different heights to measure several coronal planar dose distributions. The criterion of ? comparison between measurement and Elements was 3%/1mm and 10% threshold.
Results: between Elements and Eclipse showed a very good agreement. A mean dose difference of 12% was noticed for one shallow tumor seated right on the skull. For all other tumors, the difference between the two algorithms was within 6%, with the average difference of all tumors around 3%. Decent agreement between measurement and Elements was also obtained. For all plans, a passing rate of mid to high 90% of measurement points was achieved.
Conclusion: Elements planning system is capable of creating reliable treatment plans for deliver SRS dose to multiple brain tumors with a single isocenter. Our SRS linear accelerator is able to deliver accurate dose to patients as planned.
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