| Purpose: The objective of this site pilot study is to evaluate which radiopharmaceutical, MET or FDG, is best suited to visualise recurrent laryngeal cancer. Description: FDG has a major drawback. It also accumulates in inflammatory tissues. Residual laryngeal cancer after radiotherapy is usually embedded in inflammatory tissue. Therefore, alternatives have been sought for, e.g. in Groningen the amino acid L-1-[11C]tyrosine (TYR). Three studies have been performed. Only laryngeal and hypopharyngeal tumours were included, which makes the studies easier reproducible than most of the studies done in this field. The sensitivity and specificity of visualizing residual disease was 100%. One should however keep in mind that the number of patients included is small. A disadvantage TYR is its laborious synthesis. Methyl-labelled methionine (MET), which is chemically more readily made, yields the same favourable results as obtained with TYR. Methionine is one of the essential amino acids. After injection C-11 Methionine is rapidly distributed and a high uptake is immediately observed in the liver, kidney, pancreas and salivary glands. The uptake in tumour tissue progresses in time. MET uptake is shown in inflammation tissue, but the uptake of methionine in malignancies is significantly higher. Literature shows visualization rates of head and neck carcinoma between 90 and 100%. Squamous cell carcinoma of different sizes and locations primary and residual disease are included. These results can therefore not be extrapolated to laryngeal cancer sec. In the University Medical Center Groningen a feasibility study of MET-PET was performed in which 10 patients with a T1-2 primary laryngeal cancer were included. This study demonstrated a visualization rate of 90% (manuscript sent for publication). Moreover, the volume of most of the laryngeal cancers is small. This means the uptake within the tumour is substantial higher than the surrounding tissues in order to have the signal detected. This should make C-11 Methionine an excellent radiopharmaceutical to visualize residual laryngeal cancer as well. FDG and MET both have their advantages and disadvantages. FDG reveals anatomic details better and has a higher absolute uptake in tumour cells. C-11MET has a more consistent tumour/background ratio. Pathology is easier distinguished. FDG has a high uptake in vitro in non-vital tumour cells and macrophages. An early complete response to radiotherapy shows an abundance of non-vital tumour cells and macrophages. C-11 MET uptake is higher in fibroblasts and lymphocytes. An abundance of fibroblasts and lymphocytes is characteristic for regeneration months after the initial treatment. In our opinion C-11 MET should therefore probably be better suited to visualise residual laryngeal cancer. |
