Comparison between measured and calculated dynamic wedge dose distributions using the anisotropic analytic algorithm...

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Treatment Planning

Background:

• Accurate dose calculation is crucial for effective radiation therapy.
• The Varian Eclipse treatment planning system offers two algorithms: anisotropic analytic algorithm (AAA) and pencil-beam convolution (PBC).
• Enhanced dynamic wedges (EDW) are used to shape radiation beams, requiring precise dose modeling.

Purpose of the Study:

• To compare the accuracy of AAA and PBC algorithms in calculating 2D enhanced dynamic wedge dose distributions.
• To evaluate the performance of these algorithms for various field sizes and wedge angles.
• To determine the reliability of each algorithm for clinical treatment planning.

Main Methods:

• Measured and calculated 2D EDW dose distributions using a 60-degree photon beam from a Clinac 2300C/D linear accelerator.
• Employed ionization chambers and films for measurements.
• Utilized the Varian Eclipse 7.3 TPS with both AAA and PBC algorithms for calculations.
• Assessed accuracy using the gamma index with 3% dose variation and 3 mm distance to agreement criteria.

Main Results:

• Both algorithms accurately calculated beam axis wedge factors and percentage depth doses within 1% deviation.
• AAA and PBC reproduced measured profiles within acceptance criteria up to 30 degrees EDW.
• PBC showed significant inaccuracies for field sizes >= 10x10 cm and wedge angles of 45 or 60 degrees, particularly in high-dose regions.
• For a 20x20 cm field with a 60-degree EDW, PBC failed acceptance criteria in 28.5% of pixels, while AAA failed in only 0.48%.

Conclusions:

• The anisotropic analytic algorithm (AAA) provides significantly more accurate modeling of enhanced dynamic wedge dose distributions compared to pencil-beam convolution (PBC).
• PBC is not reliable for treatment planning with 60-degree EDW, especially for large field sizes.
• AAA is the preferred algorithm for accurate dose calculations involving EDW in Varian Eclipse TPS.