Background
Identifying tumour motion is important for radiotherapy planning of lung cancer. Minimising dose to healthy lung while ensuring sufficient dose coverage to the tumour is particularly relevant due to anatomical motion. This is typically achieved with 4DCT, which generates 3D image volumes at separately defined stages of the patient’s respiratory cycle. More recently, the introduction of commercially available 4DMRI sequences provides a potential alternative to CT based tumour motion assessment.
Aims
To compare lung tumour motion measurement using 4DMRI with 4DCT
Method
Using a prototype pulse sequence, 29 patients receiving radiation therapy for primary or metastatic malignancies in the lung, received a 4DMRI scan as part of a MRI treatment planning protocol, along with 3D and 4DCT scans. Breathing traces were used to partition 4DCT image data into 10 phase bins. 4DMRI was binned into 5 separate phases from end-inhalation to end-exhalation, using a self-navigation trace. Tumour motion was assessed using both imaging modalities including statistical analysis of breathing regularity. The technique was subsequently applied to a commercially released version of the sequence with a high-density surface coil.
Results
4DMRI showed generally good agreement with 4DCT, and in lower lobe with rapid tumour motion, appeared free from artefact or motion blurring, unlike 4DCT which was sometimes unusable. Where discrepancies were observed between the two techniques, breathing patterns analysis identified that breathing rate and regularity differences was a contributing factor. Using a commercially released 4DMRI sequence with high density receive coil, demonstrated improved image quality for both 4D and 3DMRI in lung.
Conclusion
4D imaging may provide a useful addition to a MRI protocol for lung cancer treatment planning, with benefits observed in lower lobe tumour patients in particular. Evaluation of a commercially available sequence along with a high-density surface coil, demonstrated improved image quality compared to the prototype version.