Dose calculation for asymmetric photon fields with independent jaws and multileaf collimators

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Background:

• Accurate dose calculation is critical for effective radiotherapy.
• Dual asymmetric and irregular fields pose challenges for existing dose calculation algorithms.
• Advanced treatment techniques require precise dose determination.

Purpose of the Study:

• To develop a simple and accurate method for dose calculation in dual asymmetric open and irregular fields.
• To extend existing scatter correction methods for complex field geometries.
• To validate the proposed method against measured dose data.

Main Methods:

• Developed a dose calculation method extending Kwa et al.'s scatter correction principle.
• Utilized Day's equivalent-field calculation principle.
• Determined scatter correction factors using ratios of derived doses from asymmetric to symmetric fields.
• Algorithm relies on output factors, tissue maximum ratios, and off-axis ratios.

Main Results:

• Calculated doses agreed within 0.5% of measured doses for asymmetric open fields (4 and 10 MV photon beams) at the geometric center.
• Agreement within 1% was achieved for most asymmetric irregular fields with the same geometrical center.
• The method demonstrated high accuracy for complex field configurations.

Conclusions:

• The developed method provides a simple and accurate approach for dose calculation in dual asymmetric and irregular fields.
• This technique is valuable for radiotherapy planning and delivery, especially with multileaf collimators.
• The findings contribute to improved precision and safety in radiation oncology treatments.