A revised stylized model of the adult extrathoracic and thoracic airways for use with the ICRP-66 human respiratory tract model.
The extrathoracic airways and lymph nodes have not yet been represented explicitly in mathematical or stylized models of the human body utilized in the transport of photons internally between source and target organs. Currently, the ICRP assumes that the extrathoracic airways are reasonably approximated by using the thyroid or brain as the surrogate source and target region within the ICRP 66 respiratory tract model. In the present study, a new mathematical model was created to explicitly consider the extrathoracic airways, as well as other respiratory structures in the thorax of the adult. The model incorporates the MIRD model of the adult head and neck, and the ORNL model of the adult torso/legs. Additional defining equations are established for the external nose, nasal cavity, nasal sinuses (frontal, ethmoid, sphenoid, and maxillary sinuses), oral cavity, larynx, pharynx, trachea, and main bronchi. Use of the thyroid as a surrogate source for photon emissions in the ET1 and ET2 tissues is shown to provide either close or conservative values of specific absorbed fraction to target organs such as the lungs or breasts at energies exceeding 50-100 keV. At lower energies, surrogate-region values of SAF underestimate dose to target organs in ways highly dependent upon the source/target configuration. The use of the brain as a surrogate source for ET1 and ET2 tissues irradiating the thyroid is shown to result in SAF values that are lower than values of SAF(thyroid<--ET1) by factors of approximately 2-3, and lower than values of SAF(thyroid<--ET2) by factors of approximately 30 at photon energies >50 keV. At energies <50 keV, values of SAF(thyroid<--ET2) are shown to be orders of magnitude higher than the ICRP 66 default given by SAF(thyroid<--brain).
Farfán
Eduardo B
EB
Department of Nuclear and Radiological Engineering, University of Florida, Gainesville, FL 32611-8300, USA.
Han
Eun Young
EY
Bolch
Wesley E
WE
Huh
ChulHaeng
C
Huston
Thomas E
TE
Bolch
W Emmett
WE
D000328:Adult; D001822:Body Burden; D004735:Energy Transfer / Q000502:physiology*; D006801:Humans; D008297:Male; D008954:Models, Biological; D009928:Organ Specificity; D017785:Photons; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods* / Q000592:standards; D011874:Radiometry / Q000379:methods* / Q000592:standards; D012062:Relative Biological Effectiveness; D015203:Reproducibility of Results; D012143:Respiratory Physiological Phenomena; D018570:Risk Assessment / Q000379:methods*; D012680:Sensitivity and Specificity; D013909:Thorax / Q000502:physiology*; D013961:Thyroid Gland / Q000502:physiology*