Quantitative Verification of Dynamic Wedge Dose Distribution Using a 2D Ionization Chamber Array

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Accurate dose modeling is crucial for effective radiation therapy.
• Enhanced dynamic wedges (EDW) are used to shape radiation beams.
• Treatment planning systems (TPS) require validation for specific functionalities.

Purpose of the Study:

• To investigate the accuracy of the anisotropic analytic algorithm (AAA) and pencil-beam convolution (PBC) algorithms within the Eclipse 8.9 TPS.
• To evaluate the modeling of enhanced dynamic wedges (EDW) for 6 and 18 MV photon beams.

Main Methods:

• Measurements using a 2D ionization chamber array for 6 and 18 MV photon beams.
• Gamma index analysis with acceptance criteria of 3%/3 mm and 2%/2 mm for dose differences (DD) and distance to agreement (DTA).

Main Results:

• The pencil-beam convolution (PBC) algorithm showed inaccuracies for specific field sizes (20x20 cm²) and wedge angles (60°, 45°) at 6 MV, with gamma pass rates below 90% at 3%/3 mm criteria.
• The anisotropic analytic algorithm (AAA) achieved a 2%/2 mm accuracy level.
• AAA demonstrated better agreement for 18 MV photon energy.

Conclusions:

• The anisotropic analytic algorithm (AAA) is more accurate for modeling enhanced dynamic wedges (EDW) in the Eclipse 8.9 TPS compared to pencil-beam convolution (PBC).
• Specific configurations using PBC at 6 MV require careful consideration due to observed dose modeling inaccuracies.