(Saturday, 4/4/2020) [Mountain Time (GMT-6)]
Purpose: The primary objective of this study was to clinically analyze the planning CT images, ViewRay MR images and diagnostic MR scans in order to evaluate the differences in image quality. Potential impact on tumor segmentation, and patient breathing status: free- breathing vs. maximum inhale breath hold (MIBH) vs. maximum exhale breath hold (MEBH) are discussed.
Methods: The results of ViewRay imaging QA were analyzed over 2 years and compared to diagnostic MR scanner (1.5-3 T) in radiology department over 5 years. Treatment volumes were defined on scans (kVCT, ViewRay MR and diagnostic MR) based on contrast, spatial integrity and resolution for three clinical sites: liver, sarcoma and pancreas to study contrast to noise ratio (CNR) and signal to noise ratio (SNR).
Results: All CT imaging QA tests performed over a period of three years were within tolerance limits specified by AAPM task group 66. Low contrast detectability was lower and more variable on ViewRay MR scan (µ = 27.3, s = 4.8). Slice thickness test was outside tolerance for 42% of ViewRay measurements. CNR for liver, sarcoma and pancreas were variable on ViewRay MR scanner compared to diagnostic MR but showed no significant differences. Tumor contour volume ViewRay MR scans are comparable to diagnostic scan for a study conducted for 15 patients.
Conclusion: Significant differences in imaging quality control tests performance were noted for ViewRay MR and diagnostic MR. However, CNR and SNR were acceptable on ViewRay MR images. Potential contributing factors to differences include different field strengths, pulse sequences, contrast timing and dose, radio frequency (RF) coils, and patient breathing. Further investigation is needed to understand these differences in clinically significant parameters with respect to patient motion and breathing as well as tumor regression and progression parameters.
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