11C-methionine PET, a novel method for measuring regional salivary gland function after radiotherapy of head and neck cancer

Background and purpose: Loss of salivary gland function is a distressing side-effect of radiotherapy (RT) for head and neck cancer. The aim of this study was to develop a positron emission tomography (PET) method for measuring regional salivary gland function in the major salivary glands irradiated during RT. Patients and methods: Eight head and neck cancer patients were included; two were examined before RT and six after parotid sparing RT. Patients were examined by dynamic C-11-methionine PET of the major salivary glands and parotid gland salivary flow measurements. PET data were analysed using a kinetic model of salivary gland C-11-methionine metabolism, in which salivary gland function was quantified by the net metabolic clearance of C-11-methionine, K. Functional voxel-wise images of K were calculated and matched with the CT-dose-plan for comparing regional salivary gland function with the regional radiation dose. Results: Parotid gland K correlated positively with parotid gland salivary flow, indicating that K can be used as an index of salivary gland function. K of parotid and submandibular glands was reduced dependent on the median radiation dose. In one patient, receiving a heterogeneous radiation dose to the parotid glands, regional salivary gland function was inversely correlated to the regional radiation dose. Conclusions: Salivary gland function can be measured by dynamic C-11-methionine PET. The net metabolic clearance of C-11-methionine of salivary glands was reduced dependent on the radiation dose. Dynamic C-11-methionine PET offers a method for studying the individual response of the major salivary glands to irradiation. (C) 2004 Elsevier Ireland Ltd. All rights reserved.