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UBC Theses and Dissertations

18F-FDOPA positron emission tomography and diffusion tensor imaging for radiation therapy of high-grade gliomas with dose painting Kosztyla, Robert


In the radiation therapy of high-grade gliomas, T1-weighted magnetic resonance imaging (MRI) with contrast enhancement does not accurately represent the extent of the tumour. Functional imaging techniques, such as positron emission tomography (PET) and diffusion tensor imaging (DTI), can potentially be used to improve tumour localization and for biologically-based treatment planning. This project investigated tumour localization using 3,4-dihydroxy-6-[¹⁸F]fluoro-L-phenylalanine (¹⁸F-FDOPA) PET and interhemispheric difference images obtained from DTI, and determined whether radiation therapy of high-grade gliomas using dose painting was feasible with volumetric modulated arc therapy (VMAT). First, radiation therapy target volumes obtained from five observers using ¹⁸F-FDOPA PET and MRI were compared with the location of recurrences following radiotherapy. It was demonstrated with simultaneous truth and performance level estimation that high-grade glioma radiation therapy target volumes obtained with PET had similar interobserver agreement to MRI-based volumes. Although PET target volumes were significantly larger than volumes obtained using MRI, treatment planning using the PET-based volumes may not have yielded better treatment outcomes since all but one central recurrence extended beyond the PET abnormality. The second study characterized the distribution of fractional anisotropy (FA) and mean diffusivity (MD) values obtained from DTI, as well as FA and MD interhemispheric differences. It was demonstrated that FA, MD, and interhemispheric differences approached those of contralateral normal brain as the distance from the tumour increased, consistent with the expectation of a gradual and decreasing presence of tumour cells. Lastly, a treatment planning study compared VMAT for high-grade gliomas obtained from dose painting using ¹⁸F-FDOPA PET images. Dose constraints for each contour were specified by a radiobiological model. VMAT planning using dose painting for high-grade gliomas was achieved using biologically-guided thresholds of ¹⁸F-FDOPA uptake with no significant change in the dose delivered to critical structures.

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