Dosimetric characteristics of wedged fields

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Dosimetry

Background:

• Accurate dose distribution is critical in radiotherapy, particularly for wedged fields.
• Understanding beam characteristics in non-wedged planes is essential for precise treatment planning.
• Existing methods for determining wedged field parameters can be complex and time-consuming.

Purpose of the Study:

• To investigate the beam characteristics of wedged fields in non-wedged planes for 6 MV and 15 MV X-ray beams.
• To propose and validate a simplified method for determining the maximum field length in non-wedged planes.
• To assess the impact of field size and depth on relative wedge factors for various wedge angles and beam energies.

Main Methods:

• Studied beam characteristics in non-wedged planes for 6 MV and 15 MV X-ray beams.
• Developed a measurement-efficient method to determine maximum usable wedged field lengths.
• Measured relative wedge factors for 15°, 30°, 45°, and 60° wedge filters at varying depths and field sizes.

Main Results:

• For 6 MV beams, relative wedge factors from a 10x10 cm² field size are applicable to a range of field sizes (4-20 cm²) with <1% error up to 30 cm depth.
• The 15° wedge for 6 MV beams allows a slightly larger error (0.5%) for depths up to 10 cm over the same field size range.
• For 15 MV beams, relative wedge factors for 45° and 60° lead wedges are clinically insignificant (<1%), while 15° and 30° steel wedges show <0.5% error for depths up to 10 cm across various field sizes.

Conclusions:

• The proposed method effectively determines maximum wedged field lengths for non-wedged planes with minimal measurements.
• Established guidelines for using relative wedge factors across different field sizes and depths for 6 MV and 15 MV beams.
• The findings support accurate dosimetric calculations and optimize treatment planning in radiation oncology.