3D delivered dose assessment using a 4DCT-based motion model.

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-guided Therapy

Background:

• Respiratory motion significantly complicates accurate dose delivery in lung SBRT.
• Current 4D CT-based planning may not fully capture intra-fractional motion variations.
• Precise dose calculation is crucial for optimizing SBRT efficacy and minimizing toxicity.

Purpose of the Study:

• To develop a clinically feasible method for calculating actual delivered dose distributions in SBRT for patients with significant respiratory motion.
• To improve the accuracy of dose assessment by accounting for real-time respiratory variations during treatment.

Main Methods:

• A patient-specific motion model using basis displacement vector fields (DVFs) was created from 4D CT data.
• Time-varying 3D fluoroscopic images were reconstructed from 2D kV or MV projection images using the motion model.
• Dose distributions were computed for each reconstructed timepoint, and the total delivered dose was accumulated.

Main Results:

• For regular breathing, kV and MV reconstructions showed dose errors comparable to 4D CT.
• For irregular breathing, kV and MV reconstructions yielded significantly lower dose errors than 4D CT.
• Clinical validation with patient data demonstrated the feasibility and potential differences in dose estimation.

Conclusions:

• The proposed method accurately assesses delivered doses across all respiratory phases using kV or MV projection images.
• This approach provides dose estimations comparable to 4D CT for regular breathing and superior accuracy for irregular breathing patterns.
• The technique offers a more precise method for dose evaluation in lung SBRT with respiratory motion.