Comparison between transmission and scattering spectrum reconstruction methods based on EPID images

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Background:

• Accurate photon energy spectrum reconstruction is crucial for radiotherapy quality assurance.
• Existing methods often rely on transmission or scattering data analysis.
• Electron Portal Imaging Devices (EPIDs) offer a platform for these measurements.

Purpose of the Study:

• To experimentally compare the robustness of transmission-based (Trans-based) and scattering-based (Scatt-based) photon spectrum unfolding methods.
• To determine the optimal methodology for clinical quality assurance routines.
• To validate physics-based spectrum reconstruction techniques.

Main Methods:

• Utilized EPID images of plastic blocks irradiated by a 6 MeV linear accelerator photon beam.
• Measured transmitted and scattered radiation distributions.
• Simulated radiation distributions using Monte Carlo code for monoenergetic beams.
• Developed two linear equation systems combining EPID measurements and simulations.
• Applied regularization techniques to solve for the incident photon spectrum.

Main Results:

• Both Trans-based and Scatt-based methods were developed and tested using EPID images.
• Trans-based reconstruction results demonstrated superior agreement with theoretical photon spectrum predictions.
• Scattering-based methods showed less agreement compared to transmission-based approaches.

Conclusions:

• The transmission-based method is more robust and accurate for photon spectra reconstruction.
• Trans-based spectral reconstruction is the recommended methodology for clinical quality assurance.
• EPID-based measurements combined with Monte Carlo simulations provide a viable approach for spectrum unfolding.