Iterative volume of interest based 4D cone-beam CT

Area of Science:

• Medical Physics
• Radiology
• Image Reconstruction

Background:

• 4D cone-beam CT (CBCT) is crucial for soft tissue alignment and tumor motion verification during radiation therapy.
• Conventional CBCT reconstructions suffer from streak artifacts, limiting clinical utility.
• Existing alternative reconstructions are often computationally too expensive for clinical workflows.

Purpose of the Study:

• To introduce and evaluate an iterative 4D volume of interest based (I4D VOI) reconstruction technique.
• To reduce streak artifacts and computational cost in 4D CBCT.
• To assess the performance of I4D VOI for tumor motion verification.

Main Methods:

• The I4D VOI technique was compared against standard filtered back projection (FDK), FDK with a volume of interest (FDK VOI), and total variation (TV) minimization.
• Fourteen lung cancer patient CBCT scans were used, simulating shorter scan times (2 minutes) from longer acquisitions.
• Tumor motion quantification errors and image quality were assessed using rigid registration to a gold standard motion measurement.

Main Results:

• The I4D VOI technique demonstrated comparable tumor motion quantification accuracy to other methods, with an average RMS error of 1.3 ± 0.2 mm.
• No significant difference in RMS error was found between I4D VOI and most methods, except unsmoothed FDK VOI (P = 0.02).
• I4D VOI was significantly faster than TV minimization methods, approximately 15-95 times faster.

Conclusions:

• I4D VOI and FDK VOI reconstructions offer equivalent accuracy to TV minimization for tumor trajectory measurement.
• I4D VOI provides improved bony anatomy image quality and significantly reduced computation time.
• Further research is needed to confirm the benefits of I4D VOI for tumor visualization and motion measurement through streak artifact reduction.