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Contains fulltext : 244871.pdf (Publisher’s version ) (Open Access), BACKGROUND AND PURPOSE: Magnetic resonance (MR) guided radiotherapy utilizes MR images for (online) plan adaptation and image guidance. The aim of this study was to investigate the impact of variation in MR acquisition time and scan resolution on image quality, interobserver variation in contouring and interobserver variation in registration. MATERIALS AND METHODS: Nine patients with prostate cancer were included. Four T2-weighted 3D turbo spin echo (T2w 3D TSE) sequences were acquired with different acquisition times and resolutions. Two radiologists assessed image quality, conspicuity of the capsule, peripheral zone and central gland architecture and motion artefacts on a 5 point scale. Images were delineated by two radiation oncologists and interobserver variation was assessed by the 95% Hausdorff distance. Seven observers registered the MR images on the planning CT. Registrations were compared on systematic offset and interobserver variation. RESULTS: Acquisition times ranged between 1.3 and 6.3 min. Overall image quality and capsule definition were significantly worse for the MR sequence with an acquisition time of 1.3 min compared to the other sequences. Median 95% Hausdorff distance showed no significant differences in interobserver variation of contouring. Systematic offset and interobserver variation in registration were small (<1 mm) and of no clinical significance. CONCLUSIONS: Our results can be used to effectively shorten overall fraction time for online adaptive MR guided radiotherapy by optimising the imaging sequence used for registration. From the sequences studied, a sequence of 3.1 min with anisotropic voxels of 1.2 × 1.2 × 2.4 mm(3) provided the shortest acquisition time without compromising image quality.

Contains fulltext : 244871.pdf (Publisher’s version ) (Open Access), BACKGROUND AND PURPOSE: Magnetic resonance (MR) guided radiotherapy utilizes MR images for (online) plan adaptation and image guidance. The aim of this study was to investigate the impact of variation in MR acquisition time and scan resolution on image quality, interobserver variation in contouring and interobserver variation in registration. MATERIALS AND METHODS: Nine patients with prostate cancer were included. Four T2-weighted 3D turbo spin echo (T2w 3D TSE) sequences were acquired with different acquisition times and resolutions. Two radiologists assessed image quality, conspicuity of the capsule, peripheral zone and central gland architecture and motion artefacts on a 5 point scale. Images were delineated by two radiation oncologists and interobserver variation was assessed by the 95% Hausdorff distance. Seven observers registered the MR images on the planning CT. Registrations were compared on systematic offset and interobserver variation. RESULTS: Acquisition times ranged between 1.3 and 6.3 min. Overall image quality and capsule definition were significantly worse for the MR sequence with an acquisition time of 1.3 min compared to the other sequences. Median 95% Hausdorff distance showed no significant differences in interobserver variation of contouring. Systematic offset and interobserver variation in registration were small (<1 mm) and of no clinical significance. CONCLUSIONS: Our results can be used to effectively shorten overall fraction time for online adaptive MR guided radiotherapy by optimising the imaging sequence used for registration. From the sequences studied, a sequence of 3.1 min with anisotropic voxels of 1.2 × 1.2 × 2.4 mm(3) provided the shortest acquisition time without compromising image quality.

Contains fulltext : 244871.pdf (Publisher’s version ) (Open Access), BACKGROUND AND PURPOSE: Magnetic resonance (MR) guided radiotherapy utilizes MR images for (online) plan adaptation and image guidance. The aim of this study was to investigate the impact of variation in MR acquisition time and scan resolution on image quality, interobserver variation in contouring and interobserver variation in registration. MATERIALS AND METHODS: Nine patients with prostate cancer were included. Four T2-weighted 3D turbo spin echo (T2w 3D TSE) sequences were acquired with different acquisition times and resolutions. Two radiologists assessed image quality, conspicuity of the capsule, peripheral zone and central gland architecture and motion artefacts on a 5 point scale. Images were delineated by two radiation oncologists and interobserver variation was assessed by the 95% Hausdorff distance. Seven observers registered the MR images on the planning CT. Registrations were compared on systematic offset and interobserver variation. RESULTS: Acquisition times ranged between 1.3 and 6.3 min. Overall image quality and capsule definition were significantly worse for the MR sequence with an acquisition time of 1.3 min compared to the other sequences. Median 95% Hausdorff distance showed no significant differences in interobserver variation of contouring. Systematic offset and interobserver variation in registration were small (<1 mm) and of no clinical significance. CONCLUSIONS: Our results can be used to effectively shorten overall fraction time for online adaptive MR guided radiotherapy by optimising the imaging sequence used for registration. From the sequences studied, a sequence of 3.1 min with anisotropic voxels of 1.2 × 1.2 × 2.4 mm(3) provided the shortest acquisition time without compromising image quality.

Item does not contain fulltext, BACKGROUND AND PURPOSE: Diffusion-weighted imaging (DWI) for treatment response monitoring is feasible on hybrid magnetic resonance linear accelerator (MR-linac) systems. The MRI scanner of the Elekta Unity system has an adjusted design compared to diagnostic scanners. We investigated its impact on measuring the DWI-derived apparent diffusion coefficient (ADC) regarding three aspects: the choice of b-values, the spatial variation of the ADC, and scanning during radiation treatment. The aim of this study is to give recommendations for accurate ADC measurements on Unity systems. MATERIALS AND METHODS: Signal-to-noise ratio (SNR) measurements with increasing b-values were done to determine the highest bvalue that can be measured reliably. The spatial variation of the ADC was assessed on six Unity systems with a cylindrical phantom of 40 cm diameter. The influence of gantry rotation and irradiation was investigated by acquiring DWI images before and during treatment of 11 prostate cancer patients. RESULTS: On the Unity system, a maximum b-value of 500 s/mm(2) should be used for ADC quantification, as a trade-off between SNR and diffusion weighting. Accurate ADC values were obtained within 7 cm from the iso-center, while outside this region ADC values deviated more than 5%. The ADC was not influenced by the rotating linac or irradiation during treatment. CONCLUSION: We provide Unity system specific recommendations for measuring the ADC. This will increase the consistency of ADC values acquired in different centers on the Unity system, enabling large cohort studies for biomarker discovery and treatment response monitoring.

Item does not contain fulltext, BACKGROUND AND PURPOSE: Diffusion-weighted imaging (DWI) for treatment response monitoring is feasible on hybrid magnetic resonance linear accelerator (MR-linac) systems. The MRI scanner of the Elekta Unity system has an adjusted design compared to diagnostic scanners. We investigated its impact on measuring the DWI-derived apparent diffusion coefficient (ADC) regarding three aspects: the choice of b-values, the spatial variation of the ADC, and scanning during radiation treatment. The aim of this study is to give recommendations for accurate ADC measurements on Unity systems. MATERIALS AND METHODS: Signal-to-noise ratio (SNR) measurements with increasing b-values were done to determine the highest bvalue that can be measured reliably. The spatial variation of the ADC was assessed on six Unity systems with a cylindrical phantom of 40 cm diameter. The influence of gantry rotation and irradiation was investigated by acquiring DWI images before and during treatment of 11 prostate cancer patients. RESULTS: On the Unity system, a maximum b-value of 500 s/mm(2) should be used for ADC quantification, as a trade-off between SNR and diffusion weighting. Accurate ADC values were obtained within 7 cm from the iso-center, while outside this region ADC values deviated more than 5%. The ADC was not influenced by the rotating linac or irradiation during treatment. CONCLUSION: We provide Unity system specific recommendations for measuring the ADC. This will increase the consistency of ADC values acquired in different centers on the Unity system, enabling large cohort studies for biomarker discovery and treatment response monitoring.