First-in-human clinical translation of oxygen-enhanced MRI onto an MR Linac
Dubec, Michael Datta, A. Clough, Abigael Buckley, David L Little, R. A. Berks, M. Cheung, S. Eccles, Cynthia L Higgins, D. Naish, J. H.
Dubec, Michael
Datta, A.
Clough, Abigael
Buckley, David L
Little, R. A.
Berks, M.
Cheung, S.
Eccles, Cynthia L
Higgins, D.
Naish, J. H.
Citations
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Abstract
Purpose or Objective
MR Linac (MRL) systems enable delivery of radiotherapy with on-line MRI. Functional imaging on the MRL permits
identification, mapping and tracking of tumour sub-regions, with the potential to introduce biologically adaptive
radiotherapy (Datta 2018 ClinOnc). Here we report the first application of oxygen-enhanced MRI (OE-MRI) on an MRL to
identify and map tumour hypoxia.
Materials and Methods
A dynamic 3D inversion recovery turbo field echo (IR-TFE) OE-MRI sequence was developed on a Philips Ingenia 1.5T MR
system (MRSim) in 12 healthy volunteers and 4 patients with treatment naïve head and neck (H&N) carcinoma. This protocol
was modified and implemented on an Elekta-Philips 1.5T MRL with different receive coils and required modification of
repetition and echo times due to hardware differences. Other hardware fitting steps included retrofitting of gas delivery
in the MRL bunker; installation of gas ports, delivery tubing and MR conditional blender providing 15 l/min; and installation
of a contrast agent power injector for dynamic contrast-enhanced (DCE)-MRI. Participants were recruited after providing
written informed consent on a local ethics approved protocol.
MRL OE-MRI was acquired in 4 healthy volunteers and a patient with H&N carcinoma. T1 measurement was carried out using
an IR-TFE sequence with multiple TIs and a dynamic IR-TFE series during delivery of medical air (volumes 1-25), followed
by 100% oxygen (volumes 26-70) and back to medical air (volumes 71-91). Analysis was carried out in MATLAB (Mathworks).
Native T1 maps enabled conversion of signal change to ΔR1 (where ΔR1 = R1,O2 – R1,air). In all volunteers, ΔR1 was calculated in
the nasal concha (NC). Patient tumour volumes were delineated on T1 post contrast images and ΔR1measurements obtained.
Perfused tumour voxels (DCE signal increase p<0.05) were classified as oxygen enhancing (Oxy-E) (OE signal increase p<0.05;
suggesting normoxia) or oxygen refractory (Oxy-R) (suggesting hypoxia).
Results
Volunteer NC ΔR1 was 0.059 ± 0.027 s-1 (p < 0.001, group ΔR1 change) and 0.065 ± 0.030 (p < 0.001) on the MRSim and MRL
respectively (Figure 1a-b). There was no significant difference in NC ΔR1 between the groups on the two systems (p=0.6,
unpaired t-test). Patient tumour mean ΔR1 = 0.031 ± 0.035 (p < 0.001) (n=5 patients) on the MRSim and ΔR1 = 0.035 ±
0.011 (p < 0.001) (n = 1 patient) on the MRL (Figure 1c-d). Hypoxia maps showed distinct ‘hypoxic’ and ‘normoxic’ tumour
sub-regions and are presented with the tumour ΔR1 map in figure 2. Conclusion
We have successfully translated OE-MRI onto an MRL for the first time. OE-MRI measurements in normal tissue (NC) and
tumour are consistent between the MRSim and the MRL at 1.5 T. This novel technique facilitates introduction of hypoxia
adapted radiotherapy on the MRL.
Description
Date
2022
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Dubec M, Datta A, Clough A, Buckley DL, Little RA, Berks M, et al. First-in-human clinical translation of oxygen-enhanced MRI onto an MR Linac. Radiotherapy and Oncology. 2022 May;170:S551-S2. PubMed PMID: WOS:000806764200191.