A practical method of identifying data loss in 4DCT

Abstract 

Background and purpose

The design, testing and clinical implementation of a simple quality assurance tool which allows quick and accurate identification of regions of data loss and data interpolation in 4DCT data sets is reported.

Materials and methods

A 4DCT model, dependent on gantry rotation time and pitch, was developed to allow an understanding of the data collection and reconstruction processes. To test this model, 4DCT scans of a phantom were acquired using a Siemens SOMATOM Sensation 40 slice CT scanner. A radio-opaque rod mounted under the couch top was present during the phantom scans.

Results

The model predicts that periodic regions of data loss occur when the respiration rate drops below a critical value. These results are verified by experimental data. Regions of data loss result in breaks in the imaged radio-opaque rod.

Conclusions

Regions of data loss in 4DCT data sets can be difficult to detect. Mounting a radio-opaque rod under the couch top allows regions of data loss and data interpolation to be quickly assessed on a patient by patient basis. This quality assurance tool has been successfully implemented into clinical use. The results of this work have implications for quality assurance programmes for 4DCT scanning.

Keywords: Lung cancer, 4DCT, Respiratory motion, Quality assurance, Radiotherapy