Characterizing output for the Varian enhanced dynamic wedge field

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Enhanced dynamic wedge (EDW) fields exhibit complex output factor variations dependent on field dimensions.
• The rescaling of the golden segmented treatment table (GSTT) significantly impacts output, causing over 40% change for a 60-degree wedge angle.
• Accurate output prediction is crucial for precise radiation dosimetry.

Purpose of the Study:

• To develop a simple and accurate method for predicting the output factor of enhanced dynamic wedge (EDW) fields.
• To analyze the influence of field size and moving jaw position on EDW output.
• To validate the applicability of the equivalent square method for EDW fields.

Main Methods:

• A predictive model was developed by multiplying the open field output factor with a ratio of normalized GSTT (NGSTT) values.
• NGSTT values at a reference field size (4.5 cm) and the EDW field's final moving jaw position were utilized.
• The method was tested for rectangular and asymmetric EDW fields, and compared with the equivalent square method.

Main Results:

• The output factor for EDW fields can be predicted within 1% accuracy using the proposed method.
• Separating the NGSTT factor reduces field-size-dependent wedge factor variation to less than 1%.
• The equivalent square method demonstrates similar precision for EDW fields as for open fields.

Conclusions:

• The proposed method provides a simple and accurate approach for determining EDW output factors.
• Accurate prediction of EDW output is achievable by considering GSTT rescaling and jaw positions.
• This method enhances the precision of monitor unit calculations in radiation therapy, especially for rectangular and asymmetric fields.