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Analysis of Setup Uncertainty and CTV to PTV Margin for Head and Neck Cancer Patients Using Elekta XVI Image Guidance System
Karrthick KP1*, Rajesh Thiyagarajan1 , Izaj AHAMED2 , Tamil Selvan1 , Maragatha Veni1 , Susan Abraham1 , Palanivel Duraikannu1 , T Kataria1 , (1) Medanta The Medicity, Gurgaon, Haryana, (2) Bharathiyar University, Coimbatore, Tamil Nadu.
Presentations
SU-H1-GePD-J(A)-5 (Sunday, July 30, 2017) 3:00 PM - 3:30 PM Room: Joint Imaging-Therapy ePoster Lounge - A
Purpose: Purpose of this study is to analyze the inter-fractional setup uncertainty for head and neck site using Elekta XVI image guidance system and to determine CTV to PTV margins
Methods: Total 259 CBCT image sets were acquired for 29 patients for this study. These image sets were registered with the reference image sets (planning CT image set) the resulting translational (X, Y, Z) and rotational (Pitch, Roll, Yaw) positional errors were used to estimate systematic (Σ) and random (σ) errors of the treatment delivery chain. Optimal CTV to PTV margin was calculated using Vanherk’s (2.5Σ + 0.7σ) and Stroom’s formula (2Σ + 0.7 σ)
Results: The systematic error (Σ) were 1.12mm, 1.27mm, and 0.90 mm in the lateral, longitudinal, and vertical translational dimensions, respectively, and 0.58°, 0.66°, and 0.50° in the pitch, roll, and yaw rotational dimensions, respectively. The random errors (σ) were 0.70mm, 0.68mm, and 0.77mm in the lateral, longitudinal, and vertical rotational dimensions, respectively, and 0.24°, 0.31°, and 0.25° in the pitch, roll, and yaw rotational dimensions, respectively. According to Vanherk’s and Stroom’s recipes, the recommended lateral PTV margins were 3.31mm and 2.74mm respectively; the longitudinal margins were 3.66mm and 3.02mm, respectively; and the vertical margins were 2.79mm and 2.34mm, respectively
Conclusion: Inter-fractional setup uncertainty for head and neck treatment studied and quantified. Considering both systematic and random error the setup margin required for CTV to PTV expansion is found to be 4.7mm.
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