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Summary:In 11 normal volunteers and six patients with Parkinson's disease, we compared six different analyses of dopaminergic fu nction with L-3, 4-dihydroxy-6-[18F]fluorophenylalanine (FDOPA) and positron emission tomography (PET). The caudate nucleus, putamen, and several reference regions were identified in PET images, using magnetic resonance imaging (MRI). The six analy ses included two direct determinations of DOPA decar boxylase activity (kr;, kj), the slope-intercept plot based on plasma concentration (K), two slope-intercept plots based on tissue content (k�, k�), and the striato-occipital ratio [R(n]. For all analyses, the difference between two groups of subjects (normal volunteers and patients with Parkinson's disease) was larger in the putamen than in the caudate. For the caudate nucleus, the DOPA decarbox ylase activity (kr;, kj), tissue slope-intercept plots (k;, The tracer L-3,4-dihydroxy-6-esF]fluorophenyl alanine (FDOPA) has been used widely to evaluate striatal dopaminergic functions in humans by posi tron emission tomography (PET). The enzyme aro matic amino acid decarboxylase (AAAD), or L-DOPA decarboxylase, is responsible for the re-

These results suggest that the 70% IDS plans might be beneficial for both tumour control and reducing toxicity to surrounding normal tissue if appropriate dose conformity and precise treatment set-up are ensured. The 90% IDS plans are unfavourable in view of inferior dose gradient outside the target and should be limited to cases in which the target dose homogeneity is given the highest priority.