INTERNAL DOSE ESTIMATION INCLUDING THE NASAL CAVITY AND MAJOR AIRWAY FOR CONTINUOUS INHALATION OF (CO2)-O-15, O-15(2) AND (CO)-O-15 USING THE THERMOLUMINESCENT DOSIMETER METHOD

In the steady stale method, O-15-labeled gases ((CO2)-O-15, O-15(2) an d (CO)-O-15) are administered to the body by continuous inhalation in various clinical PET studies, During inhalation, the nasal cavity and major airway may obtain a substantial amount of dose, being the source organs as well as the target organs, The internal absorbed dose to th ose organs and their contribution to the other target organs have not been calculated by the MIRD method, To calculate the internal dose in the MIRD method, the S values, the absorbed doses per unit of cumulate d activities from nasal cavity and major airway to the other organs an d vice versa, are needed, and these values are not available. Methods: In this study, we introduced a mathematical model of the nasal cavity and major airway to calculate their S values to 23 target organs and from 11 source organs to them, Individual experiments were performed t o measure the total uptake percentage and body surface doses of O-15-l abeled gases from continuous inhalation. Results: Using the body surfa ce doses measured by thermoluminescent dosimeters, the cumulated activ ities of 11 source organs were estimated with the mathematical transfo rmation method, acid then the internal absorbed doses in 23 target org ans were calculated by the MIRD method, Our experimental results were compared with the other results, and good agreements were observed, Co nclusion: Among the target organs, the critical organ is the airway, a nd the absorbed dose is 2.57 x 10(-2) mGy . MBq(-1).