Variations in tumor size and position due to irregular breathing in 4D-CT: a simulation study

Area of Science:

• Medical Imaging
• Radiology
• Computational Modeling

Background:

• Four-dimensional computed tomography (4D-CT) is crucial for accurate tumor delineation in radiation therapy planning.
• Breathing motion introduces significant artifacts and errors in 4D-CT image reconstruction.
• Quantifying these errors is essential for improving treatment accuracy.

Purpose of the Study:

• To estimate the position and volume errors in 4D-CT imaging.
• To investigate the impact of irregular breathing patterns on these errors.
• To assess the influence of tumor size and motion amplitude.

Main Methods:

• A virtual 4D-CT scanner was developed to simulate axial mode scans with retrospective sorting.
• Artificial spherical tumors were created and subjected to patient-specific breathing waveforms.
• Simulated tumors (2 and 4 cm radius) were analyzed with varying motion amplitudes (1-3 cm).

Main Results:

• Average center of mass error was <2 mm and volume error was <4% for 2 cm motion.
• Worst-case scenarios showed center of mass errors up to 1.0 cm and volume errors of 30-60% at inhale.
• Systematic errors were more pronounced for smaller tumors and irregular breathing patterns.

Conclusions:

• Irregular breathing during 4D-CT simulation leads to systematic errors in volume and center of mass measurements.
• These errors are dependent on tumor size, motion amplitude, and breathing irregularity.
• Accurate tumor characterization requires careful consideration of respiratory motion artifacts.