Cancer diagnosis with Positron Emission Tomography ; Development of a new tyrosine analogue

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The aim of study is the development of a new amino acid analogue O-[11C]methyl-L-tyrosine (OMT) and its first clinical application to whole-body imaging as well as brain tumor imaging. OMT was firstly prepared with a high radiochemical yield by the methylation of L-tyrosine with [^<11>C]methyl triflate followed by HPLC purification (Iwata et al., 2002). Later, the simple automated method using the solid phase extraction without HPLC purification was developed for routine clinical use (Ishikawa et al., 2005).Seventeen patients (13 male, 4 female, mean age 69, range 46-89) of various types of cancer or suspected of cancer with 24 lesions were studied with OMT-PET. Sixteen patients have been studied with FDG-PET also within a week.Diagnostic accuracy for all lesions were calculated as follows : sensitivity of OMT 75% (12/16) and FDG 94% (15/16) ; specificity of OMT 75% (6/8) and FDG 43% (3/7) ; and accuracy of OMT 75% (18/24) and FDG 78% (18/23). Chronic xantomatous cholecystitis showed r … More ing like uptake with FDG, but no significant uptake with OMT. Tumor to background ratios (T/B ratios) of lung cancer and brain tumor were around 2.0. Mean SUV values of malignant and benign lesions with OMT-PET and FDG-PET were as follows : OMT malignant 2.26±1.44 (n=16), OMT benign 2.25±1.33 (n=8), FDG malignant 5.98±3.38 (n=16), FDG benign 4.79±2.64 (n=7). There were no significant differences between malignant and benign neither with FDG nor OMT.As the normal distribution, liver and pancreas uptake of OMT was mild, but urinary excretion was observed from early after injection. Normal brain uptake was lower than the liver, and slightly higher than the muscle. Kidney and urine in the bladder showed the highest activity. Results were summarized as follows;1. OMT uptake by tumor was tended lower than the FDG.2. OMT uptake by inflammation was tended lower than the FDG.3. In some tumors, such as esophageal cancer, gall bladder cancer, OMT-PET may be helpful to avoid false positive results that was derived by FDG uptake of active inflammation. Less