ESTRO 2024 - Abstract Book
S3857
Physics - Image acquisition and processing
ESTRO 2024
25 patients undergo MR and CT examination at the comprehensive cancer Center Léon Bérard in Lyon. The protocol performed on a 3T Siemens Magnetom Vida MR system was 30 minutes long, including injected and non-injected T1 weighted and T2-weighted acquisitions for the delineation of OARs and the tumor and a Spiral VIBE UTE with a 30 µs echo time and a flip angle of 5° for the PD quantification. The CT scan was performed on a Siemens Somatom Go Sim. For both imaging modalities, the patient is placed on a radiotherapy table with an immobilization mask to assure positioning reproducibility, needed in radiotherapy. Lower part of the head coil and an 18 channels body coil were used. The UTE sequence with specific acquisition parameters allows to measure the PD according to the following equation: M 0 (x,y,z) = G(x,y,z) º PD(x,y,z), with M 0 the magnetization at the origin which we approximate to the UTE images and G the coils sensitivity. MR images obtained with array coils induces spatial intensity inhomogeneities in the image, which have to be corrected. We compared post-processing algorithms SENSE [6], ESPIRiT [7] and adaptive reconstruction (AR) [8] and in-line algorithms Prescan [9] and B1 filter [10] to estimated G. A phantom test allowed to determine the best estimation of G by comparing the apparent proton density to the theoretical proton density based on tubes with various percentages of H 2 O and D 2 O, invisible in proton MRI. To build the electronic density maps, we build an abacus with segmentations on the software 3D Slicer (https://slicer.org/), it is a piecewise linear regression for each type of tissue segmented. The dose planning was achieved for larynx tumor of a first patient on Monaco software [11] from CT-based images. Then, the same fluency was computed on the CT-based images. The maximum dose for OARs and the median dose for tumor volumes were compared.
Results:
The linear regressions between theoretical and measured PD gave R² of 0.88, 0.81, 0.88, 0.96 and 0.93 for SENSE, ESPIRiT, AR, Prescan and B1 filter respectively, see Figure 1.
Figure 2 shows a correspondent slice of the sCT and the CT for a male patient with a larynx tumor, with the superimposed dose planning.
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