Page 20 - Towards personalized therapy for metastatic prostate cancer: technical validation of [18F]fluoromethylcholine

Chapter 1
Whilst in the case of PET/CT, the merged modality quickly found its way in routine daily practice, PET/MRI is facing a number of technical challenges (e.g., presence of well-controlled magnetic and radio frequency fields; accurate MR-based attenuation correction maps) that never were an issue for PET/CT [27]. These issues require a high level of multidisciplinary collaboration in order to capitalize the full multiparametric potential of PET/MRI. However, the current challenge is to make PET/MRI suitable for clinical practice. Current clinical applications with PET/MRI are still in their infancy.
Radiolabeled choline
The complex and heterogeneous biology of PC poses major challenges and opportunities. The implementation of performant PET hard- and soft-ware, together with the advances in the molecular biology of PC, offer possibility for development of new imaging biomarkers and promising radiotracers. For multimodality imaging techniques (e.g., PET/CT, PET/MRI) several radiopharmaceuticals are available to detect and quantitate physiologic and metabolic pathways. The most commonly used oncological PET tracer, [18F]FDG, shows limited sensitivity for the detection of androgen dependent PC [31]. In contrast, encouraging results have been reported on the use of both 11C and 18F labeled choline derivates as PET tracers for PC [32–36].
The amino acid choline is an important precursor for the biosynthesis of phosphatidylcholine, a key component of the cell membrane phospholipids. Following transport into the cell, choline is phosphorylated by choline kinase to phosphocholine and trapped within the cell [37]. Most types of cancer, including PC, are characterized by increased choline transport and over-expression of choline kinase, in response to enhanced demand of phosphatidylcholine in highly proliferating cells [21, 38]. Because of its longer half-life (110 versus 20 minutes) and better spatial resolution due to the shorter positron range of 18F, [18F]FCH seems to be more convenient for routine clinical use than 11C-labeled choline [39]. Normal biodistribution of [18F]FCH shows relatively high uptake in the salivary glands, pancreas, liver, spleen, and kidneys; variable uptake in the bowel; and excretion into urine [40].
Since the uptake of [18F]FCH overlaps among normal, benign, and malignant prostate tissues [41], there are mixed results, with the potential utility of this radiotracer in the diagnosis and staging of primary PC [42]. At present, [18F]FCH is used mainly for
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