Physics and Radiobiology of Nuclear Medicine

Answer
The half-life of 99mTc =6 hr. The effective half-life of two biological clear-
ances are

Using Eq. (14.17)

=1.44 × 4000 ×0.99 ×(0.45 × 2 +0.55 ×3.2)

=15,200mCi · hr (0.562 GBq · hr)

Using Eq. (14.16)

D= ·S

= 15200 ×5.2 × 10 −^5

=0.79 rad

=790 mrad (7.9 mGy)

Radiation Dose in SI Units

The radiation dose in System Internationale (SI) units due to the adminis-
tration of a radiopharmaceutical can be calculated by assuming a source
volume rcontaining AMBq of the radiopharmaceutical that emits several
radiations. If the ith radiation has energy Eiand a fractional abundance Ni
per disintegration, then the energy absorbed per hour by a target of mass
mand volume vfrom the ith radiation emitted by the source volume r(dose
rate) is given by

Ri(Gy/hr) =A/m(MBq/g)NiEi(MeV/disintegration)

× 106 disintegrations/(s · MBq)

×(1.6 × 10 −^6 erg/MeV)

×(1 × 10 −^4 g · Gy/erg)

×(3600 s/hr)

=0.576 (A/m)NiEi

When the target and the source are not the same, the absorbed fraction
fi(v←r) must be taken into account. Thus,

Ri(Gy/hr) =0.576(A/m)NiEifi(v←r) (14.23)

A ̃

A ̃

Te 2

76

76

= 32

×

+

= .hr

Te 1

36

36

= 2

×

+

= hr

216 14. Internal Radiation Dosimetry