ADC measurements on the Unity MR-linac - A recommendation on behalf of the Elekta Unity MR-linac consortium
Kooreman, Ernst S; van Houdt, Petra J; Keesman, Rick; Pos, Floris J; van Pelt, Vivian W J; Nowee, Marlies E; Wetscherek, Andreas; Tijssen, Rob H N; Philippens, Marielle E P; Thorwarth, Daniela; Wang, Jihong; Shukla-Dave, Amita; Hall, William A; Paulson, Eric S; van der Heide, Uulke A
(2020) Radiotherapy & Oncology, volume 153, pp. 106 - 113
(Article)
Abstract
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
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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/mm2 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.
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Keywords: ADC, Diffusion weighted imaging, DWI, MR-linac, Recommendation, Hematology, Oncology, Radiology Nuclear Medicine and imaging, Journal Article
ISSN: 0167-8140
Publisher: Elsevier Ireland Ltd
Note: Funding Information: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: MN declares travel support from Elekta AB. DT declares institutional collaborations with Elekta, Philips, Siemens and PTW Freiburg outside of this work. The Tübingen MR-linac program is funded by the German Research Council (DFG), grants no. ZI 736/2-1 and TH 1528/6-1 . The UMCU has a long-standing research relation with Elekta and Philips. The MCW receives departmental research and travel support from Elekta. EP declares funding support from Elekta Instruments AB . UH receives research funding from Elekta AB and Philips Healthcare and ITEA project ‘Starlit’. Funding Information: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: MN declares travel support from Elekta AB. DT declares institutional collaborations with Elekta, Philips, Siemens and PTW Freiburg outside of this work. The T?bingen MR-linac program is funded by the German Research Council (DFG), grants no. ZI 736/2-1 and TH 1528/6-1. The UMCU has a long-standing research relation with Elekta and Philips. The MCW receives departmental research and travel support from Elekta. EP declares funding support from Elekta Instruments AB. UH receives research funding from Elekta AB and Philips Healthcare and ITEA project ?Starlit?. Publisher Copyright: © 2020 Elsevier B.V.
(Peer reviewed)