Cone-beam computed tomography reconstruction for a commercial proton beam therapy system

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image Reconstruction

Background:

• Cone-beam computed tomography (CBCT) is crucial for image-guided radiotherapy, enabling tracking of anatomical changes and precise patient setup.
• Accurate CBCT image reconstruction is essential for optimizing radiation delivery in proton beam therapy.
• Existing offline reconstruction methods are system-specific and often require adaptation for novel imaging systems.

Purpose of the Study:

• To develop and validate an offline methodology for reconstructing CBCT images from 2D projection data for a commercial proton beam therapy machine.
• To account for variations in exposure and beam hardening caused by gantry rotation during CBCT acquisition.
• To provide a tool for optimizing acquisition parameters and developing new reconstruction processes for proton therapy CBCT.

Main Methods:

• Acquired projection data from solid water phantoms to model bow-tie filter motion and beam hardening.
• Utilized Catphan504 phantom data and system CBCT reconstructions for method validation.
• Assessed the workflow's performance against clinical reconstructions using uniformity, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) metrics.

Main Results:

• The developed offline workflow effectively eliminated crescent artifacts in phantom and patient images, which were caused by variable exposure and beam hardening.
• The reconstructed images demonstrated signal-to-noise and contrast-to-noise ratios comparable to those from clinical system reconstructions.
• Minor differences in image quality metrics were observed and attributed to potential interplay effects within the bow-tie filter.

Conclusions:

• An effective offline CBCT reconstruction workflow was successfully developed for a commercial proton therapy system.
• This workflow serves as a valuable tool for optimizing CBCT acquisition parameters and exploring novel reconstruction techniques.
• The methodology enhances the utility of CBCT in proton therapy by improving image quality and reducing artifacts.