Difference in performance between 3D and 4D CBCT for lung imaging: a dose and image quality analysis.

Area of Science:

• Medical Physics
• Radiotherapy Imaging
• Diagnostic Radiology

Background:

• Image-guided radiation therapy (IGRT) relies on accurate imaging for precise tumor targeting.
• Three-dimensional (3D) and four-dimensional (4D) Cone-Beam Computed Tomography (CBCT) are advanced imaging techniques used in IGRT.
• Evaluating the dosimetric and image quality performance of these CBCT modalities is crucial for optimizing lung cancer treatment.

Purpose of the Study:

• To compare the performance of 3D and 4D CBCT in lung cancer radiotherapy.
• To analyze delivered dose and image quality metrics for both imaging modalities.
• To assess the impact of motion and breathing irregularities on CBCT imaging.

Main Methods:

• Analyzed 3D (Chest) and 4D (Symmetry) CBCT protocols on an Elekta XVI system.
• Measured dose profiles using thermoluminescent dosimeters (TLDs) in a phantom.
• Evaluated dosimetric indicators like cone-beam dose index (CBDI).
• Assessed image quality via contrast transfer function (CTF), noise power spectrum (NPS), and noise-equivalent quanta (NEQ).
• Simulated breathing variations to evaluate artifacts.

Main Results:

• 3D CBCT delivered twice the dose at the center compared to 4D CBCT.
• Motion significantly reduced CTF (85% for 3D, 65% for 4D CBCT).
• 4D CBCT exhibited a 50% higher NEQ than 3D CBCT under motion.
• 4D CBCT showed primarily view-aliasing artifacts, while 3D CBCT had duplication artifacts.

Conclusions:

• 4D CBCT provides better image quality and a more reasonable dose for moving targets in lung radiotherapy.
• 4D CBCT is a reliable imaging modality for lung free-breathing radiation therapy.
• The findings support the use of 4D CBCT for enhanced precision in lung IGRT.