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Evaluation of An AAA to Acuros Transition On Clinic Efficacy and Dosimetric Decision Making

L Muller

L Muller*, S Ahmad , D Johnson , Oklahoma Univ. Health Science Ctr., Oklahoma City, OK


SU-I-GPD-T-394 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: While Varian’s Acuros algorithm has been shown to calculate dose more accurately than the Analytic Anisotropic Algorithm (AAA) in regions of increasing tissue heterogeneity, this study aims to evaluate the need for changes in clinical decision making and workflow stemming from a transition from AAA to Acuros.Materials and

Methods: Preserving the beam fluence optimized with AAA, 15 clinical treatment plans (3 Thoracic, Abdominal, Cranial, Pelvic, and Head & Neck) were recalculated using Acuros for 4 treatment units and energies 6X, 6FFF, 8X, 10X, 10FFF, 15X and 18X. Dosimetric differences between AAA and Acuros plans were evaluated with gamma analysis using SNC patient. 6FFF and 15x VMAT plans were additionally re-optimized using Acuros, and compared to AAA for identical optimization objectives as AAA. All AAA optimized plans recalculated with Acuros maintained identical normalization values. PTV and organ at risk dose metrics were evaluated via DVH comparison.

Results: At isocenter, Gamma passing rates of 97.7% at 2mm/2% and 99.6% at 3mm/3% we found on average in the axial plane. Failing points were generally located near heterogeneities and high dose gradients. Plans optimized with AAA exhibit D95 values 2% lower than plans optimized with Acuros on average. Dose fall-off from D98 to D95 marginally improved when optimized with Acuros over AAA. VMAT calculations times for AAA and Acuros were equivalent for a single full rotation arc with AAA calculation times increasing linearly with number of arcs, yet remaining constant for Acuros. IMRT calculation time was found to be up to 10 times greater for Acuros.

Conclusion: Gamma analysis reveals no clinically relevant dose discrepancies between AAA and Acuros. Mixed algorithm optimization improved treatment plan quality insufficiently to warrant the increased workload. Improving accuracy and calculation time, the transition to Acuros for VMAT planning is recommended in our clinic.

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