Four-dimensional dose evaluation using deformable image registration in radiotherapy for liver cancer

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Planning

Background:

• Respiratory motion introduces uncertainties in dose delivery during radiotherapy.
• Accurate dose assessment requires accounting for organ movement during treatment.
• Four-dimensional computed tomography (4DCT) enables motion-aware radiotherapy planning.

Purpose of the Study:

• To evaluate the dosimetric impact of respiratory motion on target volumes and critical organs.
• To assess the accuracy of four-dimensional (4D) dose calculations using deformable image registration (DIR).
• To compare 4D dose distributions with conventional 3D dose calculations in free-breathing radiotherapy.

Main Methods:

• Acquired 4DCT images for 11 liver cancer patients.
• Performed 3D dose planning and calculation based on end-exhalation phase images.
• Calculated 4D dose using DIR of all 4DCT phases.
• Compared dosimetric parameters between 3D and 4D dose calculations.

Main Results:

• No significant changes in dosimetric parameters for the gross tumor volume.
• Increased mean dose and generalized equivalent uniform dose (gEUD) for the liver.
• Decreased D(max) and gEUD for duodenum, stomach, and both kidneys.
• Reduced normal tissue complication probability (NTCP) for duodenum and stomach.

Conclusions:

• 4D dose calculation accounting for respiratory motion reveals no significant difference in target coverage.
• Respiratory motion can significantly alter physical and biological dosimetric parameters for normal organs.
• Motion-aware dose assessment is crucial for optimizing radiotherapy planning and reducing toxicity.