Enhanced dynamic wedge factors at off-axis points in asymmetric fields

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Treatment Planning

Background:

• Existing methods for calculating enhanced dynamic wedge factors (EDWFs) often struggle with accuracy in large or asymmetric fields.
• Current techniques based on monitor-unit (MU) fraction methods have limitations, particularly at off-axis points.
• Beam-segment superposition methods are accurate but complex for routine clinical implementation.

Purpose of the Study:

• To develop a simple and accurate method for calculating EDWFs at off-axis points in both symmetric and asymmetric fields.
• To improve upon the limitations of existing MU fraction and beam summation methods for EDWF calculation.
• To provide a clinically applicable tool for precise radiotherapy treatment planning.

Main Methods:

• The study presents a novel calculation method based on the MU fraction approach, incorporating empirically determined field-size corrections.
• The method utilizes wedged-field profiles to estimate EDWFs, ensuring independence from calculation-point location and field symmetry.
• Measurements were conducted for 6- and 18-MV x-ray beams across various field sizes and locations to validate the proposed calculations.

Main Results:

• The developed method demonstrated high accuracy, with calculated EDWFs showing less than 2% disagreement with measurements across the clinical range.
• The maximum disagreement observed was 3% at a specific off-axis point in a large, asymmetric wedged field.
• Comparisons with the ADAC Pinnacle3 Treatment Planning System's calculations validated the proposed method's performance.

Conclusions:

• The proposed simple calculation method provides accurate estimation of EDWFs at off-axis points for symmetric and asymmetric fields.
• This technique offers a significant improvement over existing methods, enhancing the precision of radiotherapy dose calculations.
• The study discusses the strengths and weaknesses of this new method, paving the way for its potential clinical adoption.