1. Nuclear Medicine Physics
Radiation Dose
Jerry Allison, Ph.D.
Department of Radiology
Medical College of Georgia

2. Medical College of Georgia And Sameer Tipnis, Ph.D.
A note of thanks to
Z. J. Cao, Ph.D.
Medical College of Georgia
And
Sameer Tipnis, Ph.D.
G. Donald Frey, Ph.D.
Medical University of South Carolina
for
Sharing nuclear medicine presentation content

3. Definitions
Absorbed dose D (Gy): energy deposited in a unit mass of absorber
1 Gy = 1 joule/kg (SI unit)
1 rad = 100 erg/g (traditional unit)
1 Gy = 100 rad

4. Definitions
Equivalent dose HT (Sv): quantity that expresses absorbed dose across an organ or tissue with a weighting factor for type and energy of radiation
Rem (traditional unit)
1 Sv = 100 Rem
HT = DT . wR
DT: absorbed dose in a tissue
wR : weighting factor that denotes relative biologic damage for type of radiation
For x, , e- , e+ : wR = 1
For n: depends on energy
For p (> 2 MeV): wR = 2,
For a, fission fragments, heavy ions: wR = 20

5. Definitions
For organ dose in diagnostic radiology, equivalent dose (Sv) is equal to absorbed dose (Gy) since:
wR = for x, , e- , e+

6. Definitions
Effective dose E (Sv): measure of absorbed dose to whole body, the product of equivalent dose and organ specific weighting factors
Whole body dose equivalent to the nonuniform dose delivered

7. Definitions
From: International Commission on Radiological Protection: Recommendations of the International Commission on Radiological Protection. ICRP Publication 103; Ann ICRP. 37 (2-4)2007
© Physics in Nuclear Medicine: Cherry, Sorenson and Phelps

8. Definitions Dose equivalent H (Sv)
An obsolete unit that expressed absorbed dose at a point in an organ with a quality factor that depends on type of radiation
Rem (traditional unit)
1 Sv = 100 Rem
Presumably effective dose

9. Example
The “mean glandular dose” to the ACR mammographic accreditation phantom must not exceed 3 mGy (300 mRad) per view at the recommended techniques for imaging an average breast.

10. Example
What is effective dose to the patient if breasts receive an absorbed dose of 3 mGy?
wR = 1
wT = 0.12
E = D * wR * wT
E = 3 mGy * 1 * 0.12
E = 0.36 mSv
So, absorbed dose to the breasts of 3 mGy results in effective dose to the patient of 0.36 mSv (to the whole body)

11. Definitions Effective dose equivalent HE (Sv)
An obsolete unit that expressed absorbed dose to whole body, the product of dose equivalent and organ specific weighting factors
Rem (traditional unit)
1 Sv = 100 Rem
Presumably effective dose

12. Definitions
Exposure X (C/kg): charge liberated per kg of air by x- or g-rays
C/kg (SI unit)
1 R = 2.58×10-4 C/kg (traditional unit)
Measures number of ionizations

13. Definitions
Air kerma K (Gy): kinetic energy liberated per kg of air by uncharged ionizing radiations (X-rays, g-rays, neutrons)
Kinetic energy of particles liberated through
Photoelectric absorption
Compton scattering
Pair production
Gy (SI unit)
In nuclear medicine
K (Gy) = X (C/kg) * 33.7
K (Gy) = X (R) *

14. Unfortunate Caveat: In radiology: Gy and Sv are often used loosely
Rad and Rem are often used loosely
1 Gy = ~100 Rad
1Sv = ~100 Rem
1 Air Kerma Gy = 33.7 C/kg = R

15. Effective dose of NM procedures

16. Dose limits Occupational: ALARA 1 & ALARA 2 Embryo/fetus: 5 mSv total
© Physics in Nuclear Medicine: Cherry, Sorenson and Phelps