Physics and Radiobiology of Nuclear Medicine

(c) Composition of the target organ

(d) Amount of the radioactivity present in the source

(e) Shape of the source organ

5. Does the mean absorbed dose per cumulated activity,S, depend on:
   (a) Absorbed fraction
   (b) Target mass
   (c) Photon energy
   (d) Photon abundance


6. What is the important parameter that is considered in adjusting the
   activity to be administered to children compared to adults for a nuclear
   medicine test?


7. Calculate the cumulated activity in a 55-g source organ containing 3
   mCi (111 MBq) of 99mTc (t1/2=6 hr) with a biological t1/2=14 hr.


8. A target organ has a mass of 35 g and contains 1 mCi (37 MBq) of
   a radionuclide emitting a b−-particle with D 1 =0.3 g · rad/mCi · hr and
   f 1 =1.0, and a g-radiation with D 2 =0.2 g · rad/mCi · hr and f 2 =0.35.
   Calculate the mean absorbed dose per cumulated activity.


9. An external beam deposits 360 ergs of energy in 3 g of tissue. What is
   the radiation dose in rad and cGy?


10. Explain why the concept of effective dose was introduced.


11. The absorbed doses are 10 rad (10 cGy) to organ A, 5 rad (5 cGy) to
    organ B, and 6 rad (6 cGy) to organ C from each radiation from
    a 20 mCi (370 MBq) source containing two radiations having radiation
    weighting factors,Wr, as 1 and 10. The tissue weighting factors of
    organs A,B, and C are 0.30, 0.22, and 0.46, respectively. Considering
    the contribution from other organs negligible, calculate the effective
    dose.

References and Suggested Readings

Federal Register.Code of Federal Regulations. 10CFR20. Washington, DC: US
Government Printing Office; 1996.
Fourth International Pharmaceutical Dosimetry Symposium, CONF-85113, Oak
Ridge, Tenn.; November, 1985.
International Commission on Radiation Protection. 1990 Recommendations of
the International Commission on Radiological Protection;ICRP 60. New York:
Pergamon Press; 1991.
International Commission on Radiation Protection. Radiation Doses to
Patients from Radiopharmaceuticals.ICRP 80. New York: Pergamon Press;
1999.
International Commission on Radiological Protection.Radiation Dose to Patients
from Radiopharmaceuticals ICRP 53. New York: Pergamon Press; 1988.
Kereiakes JG, Rosenstein M.Handbook of Radiation Doses in Nuclear Medicine
and Diagnostic X-ray. Boca Raton, FL: CRC Press; 1980.

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224 14. Internal Radiation Dosimetry