Wedge factor dependence with depth, field size, and nominal distance--a general computational rule.

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Wedge factors are crucial for accurate dose calculations in radiation therapy.
• Understanding their dependence on various parameters is essential for clinical implementation.

Purpose of the Study:

• To investigate the dependence of wedge factors on field size, depth, and source-to-surface distance (SSD) for high-energy photon beams.
• To develop and validate a new algorithm for calculating wedge factors for clinical use.

Main Methods:

• Experimental measurements of wedge factors were performed for 4, 6, 18, and 24 MV photon beams.
• Data analysis focused on identifying trends with field size, depth, and SSD (nominal and extended).
• A new algorithm was developed based on observed dependencies and implemented in a treatment planning system.

Main Results:

• Wedge factors exhibit a general linear dependence on field size and depth.
• Wedge factor variations were found to be insignificant (< or = +/-1.0%) with respect to SSD.
• The developed algorithm accurately calculates wedge factor dependence for clinical applications.

Conclusions:

• Wedge factors are largely independent of SSD for high-energy photon beams.
• A novel algorithm effectively replaces traditional wedge look-up tables for improved dose and monitor unit calculations.
• The new algorithm enhances the accuracy and efficiency of radiation treatment planning.