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Characterization of a New Commercially Available System for Patient Specific IMRT/VMAT QA

S Stathakis

S Stathakis¹*, P Myers¹, C Esquivel¹, A Gutierrez¹, P Mavroidis², N Papanikolaou¹, (1) Cancer Therapy and Research Center, San Antonio, TX, (2) Karolinska Institutet & Stockholm University, Stockholm , Sweden

SU-E-T-341 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: To evaluate and characterize the 3D dose reconstruction algorithm of a new commercially available system for patient specific IMRT QA.

Methods: : The new Octavius 4D system and its accompanying software (Verisoft) by PTW were evaluated for the dose reconstruction accuracy.
OCTAVIUS 4D measures the dose in the isocenter. The phantom rotates synchronously with the gantry by means of an inclinometer and a motor. The collected measurements are then reconstructed to a 3D dose volume for comparison with the calculated dose in the phantom. In this study, we evaluated the 3D dose reconstruction algorithm of the system using a series of tests. Dose distributions for various field sizes, orientations, shapes and combination of fields were calculated using the Pinnacle TPS on the phantom and the respective DICOMRT dose exported to the Verisoft. Example of these fields included 3x3cm² to 25x25cm², wedged fields, AP/PA arrangements, as well as lateral fields and IMRT fields. The respective measurements were performed and comparisons were made based on gamma index, profiles and isodose distributions.


Results: The 3D gamma index ranged from 88.3 to 99.9%. Individual dose planes (axial, sagittal, and coronal) were also evaluated and their gamma was within the 3D gamma range. The new system independent of angular dependence as it rotates with gantry and the measuring array is at constant SAD and perpendicular to the beams axis.

Conclusions: The new phantom for patient specific IMRT QA in this study can effectively be used for clinical use. The ability of the software to compute 3D dose distribution from all measurements taken is powerful tool that aids the physicist to evaluate the verification plan by providing 3D information not available from other commercial systems.

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