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

250 CHAPTER 6
gamma per decay. The output data list the integral dose in an infinite medium, per
g · rads
unit of cumulated activity, in units of for each radiation. To convert from
μCi · h
the old system of units found in the MIRD publications to the SI system, that is, to
g · rads kg · Gy
go from to , we use the following relation:
μCi · h Bq · s
kg · Gy
Bq · s
kg · Gy
Bq · s
= g · rad
μCi · h ×
−3 kg Gy
10 × 10−2
g rad
4 Bq
s
3.7 × 10 × 3.6 × 103
μCi h
= g · rad
μCi · h × 75.1 × 10−14 . (6.87)
To convert from SI units to traditional units:
g · rad
μCi · h =
1 kg · Gy
×
7.51 × 10−14 Bq · s = 1.33 × 1013 ×
kg · Gy
. (6.88)
Bq · s
Now let us return to the problem. Since the 24 Na is cleared exponentially at an
effective rate λE, the amount of activity in the source organ is given by
As(t) = As(0) × e −λEt , (6.89)
where As(0) is the initial activity in the source.
∞
∞
à = As(t)dt = As(0) e −λEt As(0)
dt = . (6.90)
0
Since
λE = 0.693 0.693
=
(TR × TB)/(TR + TB)
TE
0
the biological half-life TB is found in International Commission on Radiological
Protection (ICRP) Publication 2 to be 264 hours, and the radioactive half-life TR is
15 hours, therefore
à =
λE
10 6 Bq
1.36 × 10 −5 s −1 = 7.35 × 1010 Bq · s.
Now we must calculate ϕii
The absorbed fractions, ϕi, in a number of target organs and tissues, for photons
ranging in energy from 0.01 to 4 MeV that originate in a number of different source
organs and tissues, are tabulated in Appendix A of the Journal of Nuclear Medicine,
Supplement No. 3, August 1969. 2 Table 6-8 shows the absorbed fractions from a
photon emitter that is uniformly distributed throughout the body, as in the case of
24 Na. The values of ϕi for the 1.369-MeV and 2.754-MeV gammas were found by
interpolation between values in Table 6-8 and are listed below, together with i,
2As the MIRD system evolved, the absorbed fraction was replaced by the specific absorbed fraction,
which is discussed in the following paragraph.