(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: Brainlab’s recently released Cranial SRS module provides a modulated arc option for treating cranial targets to accompany their existing dynamic conformal arc delivery of their Multiple Brain Mets Element (MME) module. Cranial SRS uses the same machine model as MME, offering the potential for immediate validation when a previous MME machine model exists. We investigated the accuracy of Cranial SRS delivery using Elekta’s Versa HD.
Methods: Cranial SRS plans were created using 6FFF beams for 8 targets sizes between 0.261cc to 17.11cc. Plans were optimized to achieve Inverse Paddick Conformity Indices (ICI) less than 1.4 and Gradient Indices (GI) less than 5. All plans were delivered to a SRSMapcheck and microDiamond in the StereoPHAN. Planar dose was evaluated using a 2%/1mm/10% threshold Relative Gamma Analysis and microDiamond measurements were directly compared to Cranial SRS predicted dose. Subsets of fields were measured with Gafchromic film in the StereoPHAN for additional dose verification.
Results: All plans satisfied ICIs < 1.4 and GIs < 5.0. Average per-plan gamma pass rates were 99.7% and average microDiamond dose differences were 0.45% for targets greater than 1.00cc and -5.22% for targets less than 1.00cc. Film measurements were within 5%/1mm of the SRSMapcheck and microDiamond results. The modulated nature of the Cranial SRS optimizer resulted in the utilization of smaller MLC field segments relative to MME where MLC apertures conform to the outline of the targets.
Conclusion: Brainlab’s Cranial SRS produces accurate modulated arc plans for cranial treatments and allows for optimization of dose to irregularly shaped targets. Additional care should be taken to verify the absolute delivered dose for targets below 1.00cc. Supplementary small field (<1cm) measurement may need to be added to an existing MME machine model when treating targets less than 2.0cc.
Keywords
Stereotactic Radiosurgery, Small Fields, Linear Accelerator
Taxonomy
TH- External beam- photons: intracranial stereotactic/SBRT
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