Introduction to Health Physics: Fourth Edition - Ruang Baca FMIPA UB

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GI Tract
13 T
RADIATION SAFETY GUIDES 383
12 T
11 T
9 8 7
9T 8T 7T BB
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6 5 4
Spt 10T 6T 5T 4T bb
3 2 1
Particles in Initial State
3T 2T 1T Particles in Transformed State
AI
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p
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t
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LNETb ETb BBb LNTHb bbb AIb Bound Material
s
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Blood
Figure 8-15. Overall compartmental model for respiratory tract clearance, including both timedependent
particle transport and absorption into the blood. Abbreviations: GI, gastrointestinal; ET,
extrathoracic; BB, bronchial; bb, bronchiolar; AI, alveolar-interstitial; LNET, lymph nodes (extrathoracic);
LNTH, lymph nodes (thoracic).
Dosimetric Model. The HRT is considered as two separate organs for dosimetric purposes.
The thoracic region is considered to be the lungs, and the ET region is
considered as one of the “remainder” tissues when we calculate the EDE. Each of
these organs consists of several different types of cells of differing radiosensitivity,
and lie at different depths below the tissue–air interface (Table 8-14). Figure 8-16
shows the modeled tube that contains the tissue–air interface and the source and
target tissues in airways in the ET, BB, and bb regions. For example, the sensitive
target cells in the bb region are the nuclei of the secretory (Clara) cells (Fig. 8-17)
that lie within the epithelial layer shown in Figure 8-16. These cells are believed to
be the progenitor cells for squamous cell carcinoma, the most frequently occurring
lung cancer. These depths are important because alphas, betas, and electrons that
are emitted from radioactive particles that are deposited on the interface surface
dissipate some of their energy in passing through the less-sensitive tissue. Thus, only
a fraction of the energy of the emitted radiation is absorbed by the sensitive target
cells. Figure 8-18 shows the absorbed fractions, AF (T←S) of beta particle energy
that is absorbed by the target cells in the bb region. ICRP Publication 66 contains
values for the AFs of all the target cells from alphas, betas, and electrons that originate
in the various parts of the respiratory tract, as well as tables of the specific AFs
of photon energy in various tissues and organs with the lungs as the source.
The HRTM is used to calculate the radiation dose to the lungs from an inhaled
radioisotope. The dose to the rest of the body from the radioactivity
transferred from the respiratory system to the blood requires knowledge of the
ET