Page 217 - Quantitative Imaging of Small Tumours with Positron Emission Tomography
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                                Chapter 11 there still are significant challenges that remain to be solved, regarding collection of large harmonized multicenter datasets for model training, external validation of radiomics versus simplified metrics, and incorporation of the available biomarkers (e.g. Gleason score, PSA, tumour stage, and PSMA expression) into a novel prediction model that will fit into clinical workflows. Future perspectives and recommendations In this thesis, we performed technical validation of small tumour quantification on PET-CT to derive biomarkers for prognostication and response assessment in prostate and lung cancer. Part of this validation included an investigation into use of artificial intelligence for quantitative PET analysis in prostate cancer. We also investigated and commented on the benefits of clinical application of these biomarkers with respect to clinical endpoints. As always in medical research, no study fills all knowledge gaps or answers all questions. Even more so, well-performed studies tend to generate more new questions than answers. Hence, using the knowledge gained in this thesis we can now comment on the future perspectives of the investigated radiotracers and use of quantitative PET biomarkers, and provide some recommendations for future research. Prostate cancer In Chapter 2 and Chapter 8, we investigated the repeatability and prognostic value of [18F]FCH PET-CT in metastatic prostate cancer (1,41). In the process of writing this thesis, choline-based ligands for prostate cancer have been (almost) entirely replaced by the novel PSMA-ligands, due to the higher detection rates for metastatic disease of the latter (49-52). Therefore, we think that [18F]FCH PET-CT will have no significant indication in future prostate cancer imaging. It may, however, be of interest for early response assessment of therapeutic PSMA- inhibitors, where PSMA PET-CT will not be feasible due to tracer competition. Whether PSMA-inhibitors will have any future as clinical drugs remains to be investigated, though (53). PSMA-ligands are the most revolutionary and successful (group of) radiotracers in nuclear medicine since the advent of [18F]FDG (54,55). Clinically, success of this tracer is greatest in the biochemical recurrence stage of prostate 216 


































































































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