Clinical Trial Details
— Status: Withdrawn
Administrative data
| NCT number |
NCT05100927 |
| Other study ID # |
21-129 |
| Secondary ID |
|
| Status |
Withdrawn |
| Phase |
|
| First received |
|
| Last updated |
|
| Start date |
January 22, 2022 |
| Est. completion date |
January 1, 2024 |
Study information
| Verified date |
January 2022 |
| Source |
Milton S. Hershey Medical Center |
| Contact |
n/a |
| Is FDA regulated |
No |
| Health authority |
|
| Study type |
Observational
|
Clinical Trial Summary
The purpose of this study is to help researchers develop MRI imaging techniques that can
provide better information for using MRI to treat cancer. MRI is a non-invasive technique
that uses magnetic fields and radio waves to create images of the inside of the body.
The investigators of this study are developing an MRI imaging technique that will help with
treatment planning for cancer patients. Specifically, the method investigating will help to
calculate how the dose the patient needs to treat his/her/their cancer is distributed. This
information is required for prescribing the dose to the patient for their cancer treatment.
Description:
Combined magnetic resonance and linear accelerator systems (MR-Linac systems) are a powerful
new cancer treatment modality. MR-Linac systems promise improved patient outcomes and
decreased side effects compared to conventional radiation therapy (RT) systems. These systems
yield exquisite soft tissue imaging, offer imaging during RT delivery, and provide a platform
for adaptive RT. However, unlike traditional RT planning with computed tomography (CT)
measured in Hounsfield units, the MR signal does not correlate with electron density.
Electron density information is required to calculate radiation dose maps for RT planning for
adaptive RT.
The MRIdian MR-Linac is a low-field system (0.35 Tesla), which is beneficial for applications
in RT because it has less effect on the radiation beam than higher field systems. However,
low-field MR systems have imaging challenges compared to high-field MR systems. The resonant
frequencies between water and fat at 0.35 Tesla are close and traditional methods of
separating these tissues (i.e., DIXON-based methods) are more difficult. Furthermore,
spectral-selection of fat is not possible, which means traditional fat saturation methods
cannot be used at 0.35T. Currently, neither a fat-saturation sequence nor a multi-echo
sequence for fat/water separation is available on the MRIdian MR-Linac system. We propose to
implement and test a fat/water separation technique optimized for 0.35T. This sequence will
enable sCT generation for MR-only simulation (i.e., RT planning without CT) and adaptive RT.
The original DIXON technique for water/fat separation depends on two signal acquisitions -
when the fat and water spins are in-phase and opposed-phase. New DIXON methods are more
flexible and enable fat/water separation at echo times that are not directly in- and
opposed-phase. At 0.35T, the fat and water spins are slow enough that the first echo (i.e.,
shortest echo) is a near-in-phase echo. Additional echoes will support a 3-point DIXON
reconstruction and B0 mapping for inhomogeneity correction.
The long-term goal of this study is to realize the benefits of MR-guided adaptive RT to
decrease toxicity and improve patient outcomes. The specific objective of this study is to
develop an MR sequence on the low-field MR-Linac for fat/water separation. For the purposes
of Radiation Oncology, multi-echo gradient-echo is a fast method to acquire a 3D stack with a
large FOV. The images can be reconstructed using a DIXON-based method to produce multiple
image types. The resulting images can be used for sCT, which could greatly assist with
auto-contouring methods and adaptive planning on MR-Linac systems. These images are also
diagnostically used for functional imaging, specifically Dynamic contrast-enhanced imaging
(DCE-MRI), which has shown promise at low field, as well as a non-contrast method magnetic
resonance angiography (MRA).
Producing these images requires chemical shift imaging. At low fields, chemical shift imaging
is difficult as the spectra of fat and water are very close (52 Hz @ 0.35T as compared to 224
Hz @ 1.5T). Traditional DIXON methods use out-of-phase and in-phase echo times (TEs) to
separate fat and water. At 0.35T, these TEs are 9.86ms and 19.7ms, respectively. However,
long TEs degrade the signal-to-noise ratio (SNR) and lead to long imaging times, particularly
for 3D stacks. In addition, B0 inhomogeneity increases and SNR degrades with longer TEs.
The hypothesis is that at 0.35T, the fat and water spins are slow enough that the first echo
(i.e., shortest echo, approximately 1ms) is a near-in-phase echo. Additional echoes will
support a 3-point DIXON reconstruction and B0 mapping for inhomogeneity correction. I predict
that once this multi-echo gradient echo sequence is implemented on the MRIdian system, it can
be used to acquire images that will successfully produce water-only, fat-only, in-phase and
opposed-phase images.
