An iterative algorithm for reconstructing incident beam distributions from transmission measurements using electronic...

Area of Science:

• Medical Physics
• Radiotherapy Physics
• Image Reconstruction

Background:

• Electronic portal imaging devices (EPIDs) are crucial for verifying radiotherapy treatments.
• Accurate reconstruction of incident radiotherapy beam profiles is essential for treatment planning and quality assurance.
• Existing methods face challenges in accounting for scatter and attenuation within phantoms.

Purpose of the Study:

• To develop and validate an iterative algorithm for reconstructing incident radiotherapy beam profiles from portal images.
• To compensate for beam attenuation and phantom scatter using a novel approach.
• To assess the accuracy and stability of the proposed reconstruction method.

Main Methods:

• An iterative algorithm was developed to extract the incident beam profile from portal images.
• The algorithm corrects for beam attenuation and subtracts scatter, using a phantom thickness map.
• Scatter was estimated via a superposition method with precalculated Monte Carlo scatter kernels.

Main Results:

• The algorithm demonstrated stable results within four iterations.
• The reconstructed incident beam distribution achieved an accuracy better than 3%.
• The method was successfully tested on homogeneous phantoms with rectangular and multileaf collimated fields.

Conclusions:

• The presented iterative algorithm effectively reconstructs radiotherapy beam profiles from portal images.
• The method provides accurate and stable results, crucial for radiotherapy quality assurance.
• This technique offers a reliable approach for verifying incident beam characteristics in clinical practice.