In oncology, PET and PET/CT with tracers beyond FDG target more specific biological processes, such as proliferation (18F-3´-fluoro-3´-deoxy-L-
thymidine;
18F-FLT), tumour
hypoxia (18F-fluoromisonidazol; 18F-
FMISO) and
phospholipid metabolism (radioactively labelled
choline derivates). FLT is a
thymidine analogue which can be labelled with 18F. PET with
18F-FLT enables to non-invasively image and to quantify the proliferation fraction of tumours. Proliferation dependent accumulation of FLT has been demonstrated for a variety of solid and haematologic
neoplasms including
lung cancer,
breast cancer,
gastric cancer,
colorectal cancer and
malignant lymphoma. Furthermore, FLT has been suggested as
surrogate marker for the assessment of response to treatment, especially when targeted drugs are utilized. PET imaging in particular has emerged as a promising non-invasive tool to accurately characterize tumour oxygenation. The great promise of PET/CT is its potential as a single imaging modality for whole body staging that provides anatomical and
biological information on the disease as a whole. It allows a more precise estimation of the hypoxic tumour volume as well as comparisons on a voxel-by-voxel basis (parametric mapping). PET and PET/CT with
hypoxia tracers thus offer the potential to optimize and individualize
therapy for patients suffering from
cancer. PET- and PET/CT-studies using 11C- or 18F-labeled
choline derivates recently have shown promising results for re-staging
prostate cancer in patients with biochemical recurrence and advanced
prostate cancer. In patients with biochemical recurrence of
prostate cancer after primary
therapy the detection rate of 11C-
choline-PET/CT shows a positive relationship with serum PSA-levels. In these patients 11C-choline PET/CT allows not only to diagnose but also to localize recurrent disease with implications on disease management (localised vs. systemic
therapy).
CONCLUSION: The clinical success of multimodal imaging with PET/CT is expected to promote the combination of MRI and PET in the future.