Email this article 
Post a Comment 
Hide
Show all
Comparison between measured vs. calculated dynamic wedge dose distributions using AAA and PBC algorithms
Abstract
Objective: To present a comparison between measured and calculated two dimensional enhanced dynamic wedge (2D EDW) dose distributions using Anisotropic Analytic Algorithm (AAA) and Pencil Beam Convolution (PBC) calculation algorithms as well as the implementation of the dynamic wedge into the treatment planning system (TPS).
Materials and methods: Measurements were carry out for a 6MV photon beam produced with a Clinac 2300C/D linear accelerator equipped with EDW. Dose distributions were calculated for square symmetric fields in a perpendicular configuration by a Varian Eclipse v7.3.1 3D TPS using both algorithms. TPS accuracy was evaluated using gamma index with the individual allowing 3% dose variation and 3mm distance to agreement (DTA) as the acceptance criteria.
Results: beam axis wedge factors and percentage depth dose calculation were within 1% deviation between calculated and measured values. In the non wedged direction, profiles exhibit variations lower than 2% of dose or 2 mm distance to agreement (DTA). In the wedge direction both algorithms reproduced the measured profiles within the acceptance criteria, 2% dose variation and 2mm DTA, up to 30° EDW. With larger wedge angles the difference increased to 3%.
Gamma distribution shows that, for field sizes of 10x10 cm or larger, using EDW of 45° or 60°, the field corners as well as the high dose region of the distribution are not well modeled by PBC algorithm. For 20x20 cm field using 60° EDW and PBC algorithm for calculation, the percentage of pixels that do not reach the acceptance criteria is 28.5% but, using the AAA algorithm for the same conditions, this percentage is only 0.48% of the total distribution. Therefore PBC is not reliable for planning a treatment when using 60° EDW for large field sizes.
Conclusions: AAA models wedged dose distributions more accurately than PBC algorithm.
Materials and methods: Measurements were carry out for a 6MV photon beam produced with a Clinac 2300C/D linear accelerator equipped with EDW. Dose distributions were calculated for square symmetric fields in a perpendicular configuration by a Varian Eclipse v7.3.1 3D TPS using both algorithms. TPS accuracy was evaluated using gamma index with the individual allowing 3% dose variation and 3mm distance to agreement (DTA) as the acceptance criteria.
Results: beam axis wedge factors and percentage depth dose calculation were within 1% deviation between calculated and measured values. In the non wedged direction, profiles exhibit variations lower than 2% of dose or 2 mm distance to agreement (DTA). In the wedge direction both algorithms reproduced the measured profiles within the acceptance criteria, 2% dose variation and 2mm DTA, up to 30° EDW. With larger wedge angles the difference increased to 3%.
Gamma distribution shows that, for field sizes of 10x10 cm or larger, using EDW of 45° or 60°, the field corners as well as the high dose region of the distribution are not well modeled by PBC algorithm. For 20x20 cm field using 60° EDW and PBC algorithm for calculation, the percentage of pixels that do not reach the acceptance criteria is 28.5% but, using the AAA algorithm for the same conditions, this percentage is only 0.48% of the total distribution. Therefore PBC is not reliable for planning a treatment when using 60° EDW for large field sizes.
Conclusions: AAA models wedged dose distributions more accurately than PBC algorithm.
Keywords
Dynamic wedges