Abstract

Peter Lind
Department of Nuclear Medicine and Endocrinology, General Hospital Klagenfurt, Klagenfurt, Austria

One of the most important current directions of PET/CT is the fact that each oncology center should run a PET/CT facility. PET/CT is on the way to be implemented as routine imaging modality at least in tumor entities such as lung cancer, head and neck cancer, lymphoma, melanoma, breast cancer, thyroid cancer and melanoma. From the technical point of view, there are new crystals such as LSO and GSO which have favourable characteristics such as short decay time and high light output. In connection with a 3D acquisition, these characteristics allow shorter imaging time for PET and therefor higher patients throughput. Whether multislice CT (eg. 16 or 64 slice CT) are of advantage with clinical relevance compared to 2 or 4 slice CT is questionable.

Future aspects of PET/CT in oncology are closely related to new F-18 labelled tracers such as F-18 Dopa, F-18 Choline or Ga-68 Dota Noc and the use of PET/CT for radiotherapy planning. F-18 Dopa is indicated in neuroendocrine tumors such as carcinoid tumors, medullary thyroid cancer or pheochromocytoma. F-18 Choline is also a reliable tracer for low grade glioma. The uptake time for F-18 Dopa in PET is usually 45-60 minutes post.intravenous injection. Fluorine-18 Choline was first sythesized in 2002 by DeGrado with slight modification by Nader in 2003. Choline is a precursor to phosphatitycholine, a cell membrane lipid. As membrane lipid synthesis is activated in prostate cancer F-18 Choline is accumulated in prostate cancer. The indication for F-18 Choline PET/CT in managing prostatic cancer is staging after biopsy confirmation of prostate cancer, localisation of the primary tumor in case of elevated PSA despite negative biopsy result, restaging after treatment in case of increasing PSA level and possibly in the future PET/CT as basis for radiotherapy planning. From technical point of view, imaging of the pelvic region should start after 1-2 minutes after injection. Otherwise for dynamic acquisition, imaging is done over 5-8 minutes. This is followed by a whole-body PET/CT acquisition 30-60 minutes after injection. In addition, a clinically potential relevant tracer for the future might be Ga-68 Data Noc for imaging neuroendocrine tumors. One of the most exciting future aspect for FDG PET/CT is the fact that using this combined imaging modality for radiotherapy planning instead of CT alone changes the GTV in 32% and the PTV in 20% of patients. It has been shown that using PET/CT for radiotherapy planning reduces the inter observer variation of volume definition. In conclusion, beyond routine clinical use of FDG PET/CT in oncology, there is a bright future with respect to new tracers and new applications especially in treatment monitoring and radiotherapy planning.