Purpose: SBRT is a standard treatment for lung metastasis. Depending on patient abilities to provide consistent breathing pattern, 4DCT scans are used to delineate ITVs, hence the image quality of 4DCT is of uppermost importance for treatment planning and can potentially affect treatment outcome. A retrospective evaluation of 4DCT image artifacts is conducted and is correlated to local recurrence.
Methods: This study uses clinical research protocol approved data of 96 patients diagnosed with lung metastases, 4DCT data sets with 10 phases were used for treatment planning, especially for the definition of the internal target volume (ITV). 4DCT artifacts were classified based on the severity of artifacts following the criteria outline in a prior study: images were classified as having minimal artifacts if they had ≤4 individual double structure artifacts at diaphragm or heart, and no interpolation artifacts in image center. Images were classified as having greater artifacts if they contained >4 individual double structure artifacts at diaphragm or heart, or any interpolation artifacts in image center. The dominant motion directions were recorded. The size of the GTV and proximity to closest artifacts were measured. Using RPM data, motion amplitude, standard deviation of patient breathing period, standard deviation of normalized patient breathing signal peak-to-peak amplitude during 4D CT acquisition are considered for covariates analysis.
Results: The local failure control was observed for 8.3% (8/96) of patients. The preliminary artifacts scoring results shows that 11 out of 42 have severe CT artifacts, 31/42 have less or equal than 3 double structure artifacts at diaphragm. No correlation was found between 4DCT artifacts and local failure.
Conclusion: Moderate 4DCT artifacts occurred in a non-negligible number of patients, however this was not found to have a measureable impact on local control. Future analysis will entail inclusion of more subjects and a multivariate analysis.