Page 17 - Towards personalized therapy for metastatic prostate cancer: technical validation of [18F]fluoromethylcholine

is predominant within individual PC patients and timely evaluating the response to 1 therapy, thus avoiding futile costly and toxic treatments.
Role of imaging in prostate cancer
Accurate diagnostic “instruments” in PC are essential, since therapeutic options vary greatly with stage and grade of the disease, specific patterns of metastatic spread (i.e., hematogeneous and/ or lymphatic) and dominant phenotype [19, 20]. Conventional imaging techniques, including transrectal ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI), are used routinely in PC, but their diagnostic accuracy is suboptimal [21]. Multimodality imaging has improved patient care over the past decade. Non-invasive, integrated positron emission tomography/ computed tomography (PET/CT) has proven to be a valuable diagnostic tool by combining in vivo metabolic and anatomic information [22]. PET/CT is used extensively in oncology for diagnosis, initial staging, restaging, therapy planning, and response monitoring of a variety of malignancies [23, 24].
PET is a functional imaging technique based on the detection of coincident photons originating from the annihilation of emitted positrons with electrons from adjacent tissues. PET uses radiotracers, which are biomolecules labeled with neutron-deficient nuclei (i.e., positron emitters). Before and upon intravenous administration of a standard dose radiotracer to the patient, the radioisotope decays, emitting a positron. After traveling a short path (1-2 mm) in tissue, the positron will annihilate with an electron, generating two 511 keV photons, which are emitted in opposite direction. PET detectors register the annihilation photons in coincidence. The spatial distribution of the radiotracer is obtained through the acquisition, storage, corrections (e.g., for the attenuation, scatter, normalization) and finally reconstruction of the emission images [25].
In an attempt to achieve accurate registration of the anatomical and functional images, the first combined PET/CT imaging system was introduced in 1998. The dual modality offers several potential advantages above the conventional imaging techniques. First of all, it fulfills a supplementary and complementary role. PET allows visualization of increased uptake of the tracer in areas which are (in)compatible with physiological biodistribution. CT, on the other hand, enables the exact localization of these areas
Introduction and outline of the thesis
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