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Internal Dose Estimation Including the Nasal Cavity and Major Airway for Continuous Inhalation of C¹⁵O₂, ¹⁵O₂and C¹⁵O Using the Thermoluminescent Dosimeter Method

Cyclotron and Radioisotope Center, Tohoku University, Aoba, Aramaki, Japan

Correspondence: For correspondence contact: Prof. T. Nakamura, Cyclotron and Radioisotope Center, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai-980, Japan.

ABSTRACT

In the steady state method, ¹⁵O-labeled gases (C¹⁵O₂,¹⁵O₂ and C¹⁵O) 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 those 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 cumulated activities from nasal cavity and major airway to the other organs and 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 to measure the total uptake percentage and body surface doses of ¹⁵O-labeled gases from continuous inhalation. Results: Using the body surface doses measured by thermoluminescent dosimeters, the cumulated activities of 11 source organs were estimated with the mathematical transformation method, and then the internal absorbed doses in 23 target organs were calculated by the MIRD method. Our experimental results were compared with the other results, and good agreements were observed. Conclusion: Among the target organs, the critical organ is the airway, and the absorbed dose is 2.57 x 10 ^–2 mGy MBq^–1.

Key Words: steady state technique • TLD • MIRD method • ¹⁵O inhalation • SAF