Individual radiation response of parotid glands investigated by dynamic 11C-methionine PET

Background and PurposePreviously, we showed that the net metabolic clearance of 11C-methionine of the parotid gland, K, calculated from dynamic 11C-methionine PET, can be used as a measure of parotid gland function. The aim of this study was to investigate by dynamic 11C-methionine PET the individual radiation dose response relationship of parotid glands in head and neck cancer patients.Patients and methodsTwelve head and neck cancer patients were examined by dynamic 11C-methionine PET after radiotherapy. Parametric images of K were generated, co-registered and compared voxel-by-voxel with the 3D radiation dose plan within the parotid gland to assess the individual radiation dose–function relationship.ResultsIn each patient, voxel-values of K decreased with increasing radiation dose. Population based analysis showed a sigmoid dose response relationship of parotid gland, from which we estimated a threshold radiation dose of 16 Gy and a mean TD50 of 30 Gy. TD50 ranged from 7 to 50 Gy in the group of patients.ConclusionsIndividual radiation dose response of parotid glands can be measured by dynamic 11C-methionine PET. The dose response analysis revealed a sigmoid relationship, a threshold radiation dose of 16 Gy, and a mean TD50 of 30 Gy.