ADC measurements on the Unity MR-linac – A recommendation on behalf of the Elekta Unity MR-linac consortium

Ernst S. Kooreman; Petra J. van Houdt; Rick Keesman; Floris J. Pos; Vivian W.J. van Pelt; Marlies E. Nowee; Andreas Wetscherek; Rob H.N. Tijssen; Marielle E.P. Philippens; Daniela Thorwarth; Jihong Wang; Amita Shukla-Dave; William A. Hall; Eric S. Paulson; Uulke A. van der Heide

doi:10.1016/j.radonc.2020.09.046

ADC measurements on the Unity MR-linac – A recommendation on behalf of the Elekta Unity MR-linac consortium

Ernst S. Kooreman, Petra J. van Houdt, Rick Keesman, Floris J. Pos, Vivian W.J. van Pelt, Marlies E. Nowee, Andreas Wetscherek, Rob H.N. Tijssen, Marielle E.P. Philippens, Daniela Thorwarth, Jihong Wang, Amita Shukla-Dave, William A. Hall, Eric S. Paulson, Uulke A. van der Heide

Radiation Physics

Research output: Contribution to journal › Article › peer-review

55 Scopus citations

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 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.

Original language	English (US)
Pages (from-to)	106-113
Number of pages	8
Journal	Radiotherapy and Oncology
Volume	153
DOIs	https://doi.org/10.1016/j.radonc.2020.09.046
State	Published - Dec 2020

Keywords

ADC
DWI
Diffusion weighted imaging
MR-linac
Recommendation

ASJC Scopus subject areas

Hematology
Oncology
Radiology Nuclear Medicine and imaging

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10.1016/j.radonc.2020.09.046

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Kooreman, E. S., van Houdt, P. J., Keesman, R., Pos, F. J., van Pelt, V. W. J., Nowee, M. E., Wetscherek, A., Tijssen, R. H. N., Philippens, M. E. P., Thorwarth, D., Wang, J., Shukla-Dave, A., Hall, W. A., Paulson, E. S., & van der Heide, U. A. (2020). ADC measurements on the Unity MR-linac – A recommendation on behalf of the Elekta Unity MR-linac consortium. Radiotherapy and Oncology, 153, 106-113. https://doi.org/10.1016/j.radonc.2020.09.046

Kooreman, ES, van Houdt, PJ, Keesman, R, Pos, FJ, van Pelt, VWJ, Nowee, ME, Wetscherek, A, Tijssen, RHN, Philippens, MEP, Thorwarth, D, Wang, J, Shukla-Dave, A, Hall, WA, Paulson, ES & van der Heide, UA 2020, 'ADC measurements on the Unity MR-linac – A recommendation on behalf of the Elekta Unity MR-linac consortium', Radiotherapy and Oncology, vol. 153, pp. 106-113. https://doi.org/10.1016/j.radonc.2020.09.046

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title = "ADC measurements on the Unity MR-linac – A recommendation on behalf of the Elekta Unity MR-linac consortium",

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 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.",

keywords = "ADC, DWI, Diffusion weighted imaging, MR-linac, Recommendation",

author = "Kooreman, {Ernst S.} and {van Houdt}, {Petra J.} and Rick Keesman and Pos, {Floris J.} and {van Pelt}, {Vivian W.J.} and Nowee, {Marlies E.} and Andreas Wetscherek and Tijssen, {Rob H.N.} and Philippens, {Marielle E.P.} and Daniela Thorwarth and Jihong Wang and Amita Shukla-Dave and Hall, {William A.} and Paulson, {Eric S.} and {van der Heide}, {Uulke A.}",

note = "Publisher Copyright: {\textcopyright} 2020 Elsevier B.V.",

year = "2020",

month = dec,

doi = "10.1016/j.radonc.2020.09.046",

language = "English (US)",

volume = "153",

pages = "106--113",

journal = "Radiotherapy and Oncology",

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T1 - ADC measurements on the Unity MR-linac – A recommendation on behalf of the Elekta Unity MR-linac consortium

AU - Kooreman, Ernst S.

AU - van Houdt, Petra J.

AU - Keesman, Rick

AU - Pos, Floris J.

AU - van Pelt, Vivian W.J.

AU - Nowee, Marlies E.

AU - Wetscherek, Andreas

AU - Tijssen, Rob H.N.

AU - Philippens, Marielle E.P.

AU - Thorwarth, Daniela

AU - Wang, Jihong

AU - Shukla-Dave, Amita

AU - Hall, William A.

AU - Paulson, Eric S.

AU - van der Heide, Uulke A.

PY - 2020/12

Y1 - 2020/12

N2 - 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/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.

AB - 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/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.

KW - ADC

KW - DWI

KW - Diffusion weighted imaging

KW - MR-linac

KW - Recommendation

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SN - 0167-8140

VL - 153

SP - 106

EP - 113

JO - Radiotherapy and Oncology

JF - Radiotherapy and Oncology

ER -

ADC measurements on the Unity MR-linac – A recommendation on behalf of the Elekta Unity MR-linac consortium

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