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Producing high quality cranial SRS plans with 4Pi planning technique in a commercial clinical solution
Ganesh Narayanasamy1, Nishan Shrestha1, Milan Bimali2
1Department of Radiation Oncology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USA.
Purpose:
To generate high-quality stereotactic radiosurgery (SRS) plans for single cranial lesions using 4Pi planning technique and compare these to our clinical "status quo" plans.
Methods:
Eighteen vestibular schwannoma (VS) patients previously planned with Varian Eclipse RapidArc and treated on a Varian TrueBeam using 6FFF MV photon beams were randomly selected. This cohort was replanned in Brainlab Elements Cranial SRS using an automatic 4Pi trajectory optimization technique ("Elements 4Pi"). "Elements ArcMatch" plans were also created, which utilized the identical arc geometry as the clinical plans in Eclipse, that is, used identical table angles, gantry start and stop angles, and collimator angles to isolate the inherent differences between the two treatment planning systems. SRS plan evaluation metrics included the Inverse Paddick conformity index (IPCI), gradient index (GI), max doses to the brainstem and ipsilateral cochlea, and number of monitor units (MUs). Pairwise comparisons between Eclipse and Elements 4Pi plans were performed using Wilcoxon signed rank test. For three-way comparisons with Elements-ArcMatch plans, the difference in distribution of SRS metrics was assessed first based on Friedman's test, followed by pairwise comparison if the findings from Friedman's test met statistical significance. A two-sided p-value of 0.05 was used to determine statistical significance.
Results:
While both Elements 4Pi and Elements ArcMatch plans had significantly lower GI, MU, and max doses to the brainstem and ipsilateral cochlea compared to Eclipse plans (p-values < 0.05), Elements 4Pi also had significantly lower IPCI values.
Conclusion:
The automation in Brainlab Elements Cranial SRS outperformed manual expert planning and produced collision-free and clinically deliverable plans for single targets with significantly better dose conformality, dose gradient, and lower dose to normal organs while using lower MUs compared to clinically delivered Eclipse plans.
