Program Information
Dosimetric Influence of Jaw Tracking Option On Lung SBRT Using VMAT and IMRT Techniques
A Amoush1*, S Ferjani2 , (1) Augusta University, Augusta, GA, (2) Saint Lukes Health System, Kansas City , MO
Presentations
TU-C1-GePD-T-5 (Tuesday, August 1, 2017) 9:30 AM - 10:00 AM Room: Therapy ePoster Lounge
Purpose: To investigate the dosimetric influence of jaw tracking (JT) for lung SBRT using VMAT and IMRT techniques.
Methods: Output factors (OF) were measured for static fields between 0.5 x 0.5-3 x 3 cm2 on Varian Edge machine equipped with 6MV, 10MV, 6MVFFF, and 10MVFFF. Static fields were defined by jaws with MLCs retracted and by MLCs with fixed jaws and measurements performed with mircoionization chamber. Results were compared to the predicted dose by Eclipse 11.0 TPS. Eight VMAT/IMRT lung SBRT patients treated with 6MVFFF were retrospectively selected for this study. For the VMAT technique, four patients were replanned with and without the JT option to deliver the same dose. For IMRT technique, four patients were recalculated with and without the JT option to achieve the same prescription. Point dose and gamma analyses were compared for all plans.
Results: Using static MLCs, the average deviation from TPS for all energies was 3.1%±0.2% and 7.4%±2.1% for 1x1-3x3 cm2 and 0.5x0.5, respectively. Using static jaws, the average deviation was 1.3%±0.2%, 7%±1.8%, and 59%±3.4 for 2x2-3x3, 1x1, and 0.5x0.5 cm2, respectively. For lung SBRT using VMAT technique, the average deviation between the measured and predicted dose point dose was 0.54%±0.01% using JT and 0.43%±0.01% without JT (ρ=0.85). For Gamma analyses using 3mm/3%, the average pass rate was 97.1%±3.1% using JT and 99.9%±0.85% without JT (ρ=0.1). Using IMRT technique, the average point dose deviation was 0.75%±0.004% using JT and 1.2%±0.003% without JT (ρ=0.37). The average gamma pass rate using 3mm/3% was 83%±10.8 using JT and 81.0%±11.2% without JT (ρ=0.88).
Conclusion: TPS predicted the OF accurately down to 1x1 cm2 using MLCs and down to 2x2 cm2 using jaws. For lung SBRT with VMAT or IMRT techniques, the average point dose and film dosimetry showed no significant differences between plans with and without JT.
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