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  4. Quality Assurance Study of Stereotactic Radiosurgery of Multiple Brain Lesions with a Single Isocenter

Quality Assurance Study of Stereotactic Radiosurgery of Multiple Brain Lesions with a Single Isocenter

J Zhang*, J Rahimian , S Lee , W Lien , J Han , D Kim , K Goldman , S Lu , G Hong , Y Qian , Southern California Permanente Medical Group, Los Angeles, California

Presentations

(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: We have recently commissioned a commercially available treatment planning software capable of simultaneous SRS treatment of multiple brain lesions with a single isocenter. The treatment plans are optimized to deliver the prescription dose to each lesion based on our predefined dose-volume histogram. The plan optimization is done using preset couch positions to deliver between 5 to 14 dynamic conformal arcs. The purpose of this study was to compare two different patient specific plan QA methods from Sun Nuclear ArcCheck with insert and MapPhan.

Methods: We defined 5 lesions with 0.10, 0.29, 0.37, 0.62 and 1.58cm³ volumes in a CT image of a head phantom. A treatment plan was made using seven dynamic conformal arcs with 5 couch positions and 6MV Flattening Filter Free beams. The Conformity Index (CI) for each of the lesions were 1.60, 1.53, 1.45, 1.67 and 1.38. The plan was mapped to an ArcCheck and a MapPhan diode array system. The measured and planned absolute and relative dose distributions were compared with dose to agreement criteria of 3%/1mm, 3%/2mm, and 3%/3mm.

Results: The pass rates for the MapPhan measurement were 92.1%, 96.7% and 97.7% with the 3%/1mm, 3%/2mm and 3%/3mm dose to agreement criteria, respectively. The pass rates for the ArcCheck were 89.7%, 97.2% and 99.1%, respectively. The planar dose distribution from MapPhan shows the dose distribution for 5 lesions individually while the ArcCheck provides the 3D dose distribution only. Through Sun Nuclear advanced features, the measurement spatial density resolution can be doubled for the ArkCheck, however, the pass rate is similar.

Conclusion: The results from MapPhan and ArcCheck are comparable, therefore, either one can be used to evaluate the accuracy of the absolute and relative dose distribution for the single isocenter-multiple lesions SRS in the clinic.

Keywords

Quality Assurance, Stereotactic Radiosurgery

Taxonomy

TH- External beam- photons: intracranial stereotactic/SBRT

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