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

400 CHAPTER 8
Section of GI Tract
Stomach (ST) 150
Small Intestine (SI)
Upper Large Intestine (ULI)
Lower Large Intestine (LLI)
Ingestion
Stomach (ST)
Small Intestine (SI)
Upper Large
Intestine (ULI)
Lower Large
Intestine (LLI)
λLLI Excretion
Mass of
Walls
(g)
640
210
160
λ ST
λ SI
λ ULI
λ B
Mass of
Contents
(g)
250
400
220
135
Body fluids
Mean Residence
Time
(d)
1/24
4/24
13/24
24/24
λ
(d −1 )
Figure 8-19. Dosimetric model of the gastrointestinal tract. The clearance rate for transfer from the
small intestine into the body fluids is given by Eq. (8.42). (Reproduced with permission from ICRP
Publication 30, Part 1: Limits for Intakes of Radionuclides by Workers. Ann ICRP. 1979; 2(3/4):33.
Copyright c○ 1979 International Commission on Radiological Protection.)
Gastrointestinal Tract
In cases of ingested radionuclides or radionuclides transferred to the GI tract from
the lungs, and especially for those nuclides that are poorly absorbed from the GI
tract, the GI tract or portions of it may be the tissue or organ that receives the greatest
dose. The dose to the GI tract is calculated on the basis of the four-compartment
dosimetric model shown in Figure 8-19. According to this model, the radionuclide
enters the stomach (ST) and then passes sequentially through the small intestine
(SI), from which most absorption into the body fluids occurs. It then passes through
the upper large intestine (ULI) and the lower large intestine (LLI). Finally, the
remaining activity is excreted in the feces. The clearance rate for transfer from the
small intestine into the body fluids is given by
24
6
1.8
1
λB = f1λSI
, (8.42)
1 − f1
where f1 = fraction of the stable element reaching the body fluids after ingestion.
In making dose calculations for the purpose of calculating a DC and an ALI,
we assume the radionuclide to be uniformly distributed throughout the contents
of the respective segments of the GI tract and the weight of the contents of each