Feasibility of magnetic resonance imaging-based radiation therapy for brain tumour treatment
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Perustieteiden korkeakoulu |
Master's thesis
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Authors
Date
2017-08-21
Department
Major/Subject
Biomedical Engineering
Mcode
SCI3059
Degree programme
Master’s Programme in Life Science Technologies
Language
en
Pages
79+8
Series
Abstract
Purpose : The increasing use of MRI alongside CT images has brought about growing interest in trying to determine radiation attenuation information based on MR images only. The primary aim of this thesis is, therefore, to determine what head tissue compartments need to have separate HU values in order to obtain sufficient RT planning accuracy. This can serve as input for an MR-based classification thus enabling pseudo-CT generation in an MR-only RT workflow. Methods: To achieve this target, flattened (stratified) CT images (fCT) were generated and compared to the original CT images. Mean (ME) and mean absolute (MAE) errors were used for the fCT quality assessment, as was dose comparisons. 70 CT-based RT plans were generated and the dose distributions compared to those obtained when using the different fCT versions in place of the original CT images. The dose agreement was assessed using DVH and 1%/1mm gamma analysis. Results: The lowest MAE of 59.63 HU was calculated for an fCT8 version. DVH analysis showed low differences in the range between 3% (water-filled fCT) and 0.05% depending on the tissue stratification of the fCT version. 1%/1mm gamma analysis correctly identified plans where insufficiently fine-grained tissue classification was the main reason for dose discrepancy. The best RT planning accuracy was obtained for the fCT5 with segmented air cavities, fat, water-rich tissue, spongy, and compact bone, and for the fCT8 where also the brain tissue was stratified. Conclusions: The small differences in dose accuracy between CT and fCT images shows the feasibility of using MR-only RT planning for the brain. Nonetheless, other aspects of the MR-only workflow, such as patient positioning, as well as the impact of e.g. the surgical incisions in the skull should be subject to further research.Description
Supervisor
Ilmoniemi, RistoThesis advisor
Köhler, MaxKeywords
radiotherapy, MR-only, brain tumour, tissue stratification, RT planning, dose comparisons