Room: AAPM ePoster Library
Purpose: Single-isocenter multiple-target (SIMT) stereotactic radiosurgery has been used clinically to treat brain metastasis using a fixed MLC margin of up to 1mm around the target to optimize dose conformity. Advances in Brainlab’s SIMT optimization now allow both positive and negative MLC margins that can vary for each arc to optimize both target conformity and normal tissue sparing. An analysis was performed to determine the new optimizations effect on SIMT plan metrics and dosimetric accuracy was verified.
Methods: Previously treated clinical SIMT plans were re-optimized using the proposed new algorithm for 9 patients with 41 targets ranging in size from 0.06cc to 19.41cc. All re-plans were normalized to at least 95% target coverage and used the same couch angles to match initial clinical objectives. Plan quality was evaluated using: inverse Paddick Conformity Index (iCI), Gradient Index (GI), minimum dose to the PTV (PTVmin), and volume of the whole brain receiving 12Gy (WBV12). A student t-test was used to compare plan quality metrics for the two optimizations. Finally, a subset of the plans were delivered to an SRSMapcheck and microDiamond in a StereoPHAN on a Versa HD to verify dose.
Results: The new optimization algorithm reduced iCI by 0.05 +/- 0.10 [P < 0.01] and GI by 0.40 +/- 0.65 [P < 0.01], with no significant changes to the PTVmin [P > 0.10]. WBV12 was reduced by an average of 8.54% +/- 3.18% [P < 0.01]. Average SRSMapcheck pass rates were 98.7% [97.0% - 99.8%] using relative gamma analysis (2%/1mm/10% threshold). Measured microDiamond doses were within 1.40% of calculated for all targets.
Conclusion: Brainlab’s new SIMT algorithm, utilizing variable MLC margins to optimize both iCI and GI, improves target metrics and normal tissue sparing with good dosimetric delivery accuracy. The algorithm has been commissioned for clinical use.