Deviations in delineated GTV caused by artefacts in 4DCT

Area of Science:

• Medical Imaging
• Radiation Oncology
• Radiotherapy Planning

Background:

• Four-dimensional computed tomography (4DCT) is crucial for breathing-adapted radiotherapy planning.
• Artefacts in 4DCT can arise from irregular breathing, large tumour motion, or image interpolation.
• These artefacts can potentially affect the accuracy of gross tumour volume (GTV) delineation.

Purpose of the Study:

• To evaluate the impact of 4DCT artefacts on the measured size of the gross tumour volume (GTV).
• To determine if tumour motion or breathing signal variations contribute to GTV size discrepancies within 4DCT scans.

Main Methods:

• GTV was delineated in all temporal bins of 19 4DCT scans from patients with lung tumours.
• Variations in GTV size across bins were analyzed and correlated with tumour motion and breathing signal characteristics.
• Intra-session delineation error was assessed through re-delineation.

Main Results:

• In 16 scans, GTV size deviations from the end-expiratory reference exceeded delineation error.
• Largest GTV variations occurred in bins near end-inspiration.
• GTV size variation significantly correlated with cranio-caudal tumour motion, but not breathing signal variations.

Conclusions:

• Significant variations in GTV size exist within 4DCT scans due to artefacts.
• Radiotherapy planning based on a single 4DCT bin may be inaccurate.
• Awareness of artefact-induced errors is critical for precise GTV definition in radiotherapy.