SU-FF-T-318: Measured Versus Calculated Dynamic Wedge Dose Distribution Using Anisotropic Analytic Algorithm (AAA) and Pencil Beam Convolution (PBC) Algorithms

Purpose: The purpose of this work is to compare measured and calculated 2D EDW dose distributions using AAA and PBC calculations algorithms. Method and Materials: A 6MV photon beam from a Clinac 2300C/D Linac equipped with 7 EDW was used. Dose distributions were calculated for square symmetric fields by a Varian Eclipse v7.3.1 3DTPS with AAA and PBC algorithms. EDW were commissioning in the TPS. Dose distributions were measured using Kodak EDR2 films in a perpendicular configuration at 5cm depth in a solid water phantom for 4×4, 10×10, 15×15 and 20×20 cm field size settings. TPS calculations were performed for the same conditions as measurements, using a phantom with the same geometry. Calculation grid was 2.5×2.5 mm for PBC and 1×1 mm for AAA. Dose distributions were compared using RIT v4.3 software with gamma evaluation using 3% dose variation and 3mm DTA criteria. Results: Measured versus calculated percentage depth doses and wedge factors agree within 1%. Profiles in the non wedged direction, exhibit variations lower than 2% of dose or 2 mm DTA. In wedged direction both algorithms reproduces the measured profiles with deviations smaller than 2% of the normalization dose except in the penumbra region. AAA algorithm models better the penumbra region. EDW with angle lower than 45°, both algorithms model the distributions within the acceptance criteria. Some differences could be seen in the corners of the beams. For EDW with 60° angle, the percentage of pixels that not passes the acceptance criteria using AAA is acceptable, but using the PBC algorithm the percentage must be considered (reaching 28.5% of the distribution), representing regions of disagreement that may be of clinical interest. Conclusions: AAA algorithm models EDW dose distributions better than PBC. Differences between both algorithms increase with field size.