Comparison between measured and calculated dynamic wedge dose distributions using the anisotropic analytic algorithm and pencil‐beam convolution

Abstract

We used the two available calculation algorithms of the Varian Eclipse 7.3 three‐dimensional (3D) treatment planning system (TPS), the anisotropic analytic algorithm (AAA) and pencil‐beam convolution (PBC), to compare measured and calculated two‐dimensional enhanced dynamic wedge (2D EDW) dose distributions, plus implementation of the dynamic wedge into the TPS. Measurements were carried out for a 6‐MV photon beam produced with a Clinac 2300C/D linear accelerator equipped with EDW, using ionization chambers for beam axis measurements and films for dose distributions. Using both algorithms, the calculations were performed by the TPS for symmetric square fields in a perpendicular configuration. Accuracy of the TPS was evaluated using a gamma index, allowing 3% dose variation and 3 mm distance to agreement (DTA) as the individual acceptance criteria. 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 DTA. In the wedge direction, both algorithms reproduced the measured profiles within the acceptance criteria up to 30 degrees EDW. With larger wedge angles, the difference increased to 3%. The gamma distribution showed that, for field sizes of 10×10 cm or larger, using an EDW of 45 or 60 degrees, the field corners and the high‐dose region of the distribution are not well modeled by PBC. For a 20×20 cm field, using a 60‐degree EDW and PBC for calculation, the percentage of pixels that do not reach the acceptance criteria is 28.5%; but, using the AAA 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 a 60‐degree EDW for large field sizes. In all the cases, AAA models wedged dose distributions more accurately than PBC did.PACS numbers: 87.53.Bn, 87.53.Dq, 87.53.Kn

Validation of Varian's AAA algorithm with focus on lung treatments

“…For these simple fields, we do also find deviations below 2%. For the wedged fields, we found deviations up to 3% in the 2D dose distribution, in accordance to the findings of Caprile et al [18]. Finally, Van Esch et al [12] found deviations below 1.5 and 3% for asymmetric wedged fields and IMRT fields, respectively.…”

“…Patient specific treatment plans were created and the dose distribution of static and dynamic fields were measured for each separate field for G 00 o . When AAA is configured, it is possible manually to optimize three parameters to improve the calculations of fields with EDW [11,18]. We optimized these parameters.…”

Dose Validation of Physical Wedged Asymmetric Fields in Artiste Linear Accelerator

“…The highest difference of our results is higher than Venselaar and Welleweerd and lower than Caprile et al [26] which riches to 28.5% for pencil-beam convolution (PBC) for field size 20 × 20. The disagreement regions correspond to the edge of the field where the penumbra is not well modeled.…”

Technical Note: Initial characterization of the new EBT‐XD Gafchromic film

“…All measurements were compared to TPS calculations from the Varian Eclipse Analytical Anisotropic Algorithm (version 11.0.31) which has been shown to adequately model EDW delivery. 16 To evaluate energy dependence, EBT-XD films were exposed to doses of 400, 600, 850, 1200, 1600, 2200, and 3000 cGy using 6 and 18 MV beams. Films were placed at the respective depth of maximum dose for each energy and irradiated at a source-to-surface distance of 100 cm using 10 × 10 cm 2 fields.…”