A convolution method for constructing primary beam profiles in the presence of beam modifiers.

Area of Science:

• Medical Physics
• Radiotherapy Physics
• Computational Physics

Background:

• Current radiotherapy treatment planning systems often simplify finite source size effects, particularly for beams modified by blocks, wedges, or filters.
• Accurate modeling of the primary beam profile is crucial for effective radiotherapy dose calculations.

Purpose of the Study:

• To develop a method for incorporating extended source effects into radiotherapy beam profiles, consistent with unmodified beams.
• To provide a framework for calculating the impact of beam modifiers on primary beam profiles considering source characteristics.

Main Methods:

• The unmodified beam profile is represented as a convolution of an unknown source function and a collimator transmission profile.
• Fourier transforms are employed to solve for the unknown source function.
• The derived source function is then convolved with modified beam transmission profiles (blocks, wedges, filters) to determine the final primary beam profile.

Main Results:

• A method was established to accurately calculate primary beam profiles by deconvoluting the source function from unmodified beams and reconvoluting it with modified beam transmission profiles.
• The approach allows for consistent treatment of extended source effects across both modified and unmodified beams.
• Examples demonstrating the calculation of beam modifier effects on primary beam profiles were successfully generated.

Conclusions:

• The proposed Fourier transform-based method effectively accounts for extended source characteristics in radiotherapy beam profiles, even when beam modifiers are present.
• This technique enhances the accuracy and consistency of dose calculations in radiotherapy treatment planning.
• The findings support improved precision in radiation delivery for cancer treatment.