An MRI comparative image evaluation under diagnostic and radiotherapy planning set-ups using a carbon fibre tabletop for pelvic radiotherapy.

PURPOSE: To quantitatively and qualitatively evaluate and compare MR images acquired from the usual diagnostic set-up with images acquired in a radiotherapy set-up. MATERIALS AND METHODS: MR images of a phantom and 18 prostate cancer patients imaging using the usual diagnostic set-up with a curved tabletop (DX-set-up) and using a radiotherapy set-up (RT-set-up) with a flat tabletop, were analysed retrospectively. Quantitative assessments were made by measuring signal-to-noise ratio (SNR) and contrast to noise ratio (CNR). Non-parametric tests were used. Qualitative assessments were made independently by three radiologists. Inter-rater reliability was measured as the percentage of agreement and Gwet's AC2 test. RESULTS: The use of the RT-set-up was linked to 19.3% SNR drop on the phantom image. Up to 24% SNR prostate drop was observed in patients' images. Up to 34% CNR drop was observed in patients' images. Although image quality of the RT-set-up was acceptable, all measured domains were worse than the corresponding DX-set-up. Additionally diagnostic images were linked to a better percentage of agreement among raters. CONCLUSIONS: SNR, CNR and image quality were significantly worse when using the RT-set-up than with the DX-set-up although Image quality in the RT-set-up was acceptable.