1. Nuclear Medicine Physics
Radiation Protection in Nuclear Medicine
Jerry Allison, Ph.D.
Department of Radiology & Imaging
Medical College of Georgia
Augusta University

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. Information for Patients Administered Radioactive Iodine (I-131)

4. Radiation exposure of the public

5. Sources of low-dose radiation
1982 data of NCRP: 4.6 mSv/person/yr
Natural background: 4 mSv/person/yr (88%)
Radon at home: 2.57 mSv/person/yr (56%)
Other sources: 1 mSv/person/yr (22%)
e.g. U-238 and Th-232 in soil, cosmic rays from the sky, and internal radiation from 40K, 14C and 3H
Fallout from nuclear power stations and consumer products: 0.46 mSv/person/yr (10%)
Medical: 0.54 mSv/person/yr (12%)

6. Sources of low-dose radiation
2006 data of NCRP: 6.7 mSv/person/yr
Natural background: 3.5 mSv/person/yr (52%)
Dramatic increase of medical dose from to 3.2 mSv/person/yr (12%  48%)
CT dose: ~ 1.6 mSv/person/yr (50% of medical)
NM dose: ~ 0.8 mSv/person/yr (25% of medical)
Dramatic increase of NM and CT studies:
NM 6 M M (3% of all)
CT M M (12% of all)
Average CT dose: 20 mSv

7. Radiation dose effects

8. Stochastic and non-stochastic effects
Stochastic: The frequency of effects in a
population depends on dose without
threshold (e.g. cancer).
Non-stochastic: The severity of effects varies with dose above threshold (e.g. cataracts).
Aim of radiation protection: to prevent non-stochastic effects by limiting the radiation dose received as well as to reduce the probability of stochastic effects through ALARA practice.

9. Models of low-dose response
Lack of certainty for low dose effects (< 1 Sv/yr)
Linear no threshold (LNT) model: a line connecting the bottom end of high-dose response curve to the zero dose
Linear-quadric model: linear for the lowest dose and quadric for the remainder
Hormesis model: ‘J’ shape  dangerous at high dose but beneficial at low dose, low dose sterilizing cancer cells and stimulating cell activities

10. Models of low-dose response
damage
high dose data
linear
linear+quadric
1 Sv/yr
dose
hormesis
benefit

11. Internal dosimetry Factors determining internal dose
Medical internal radiation dosimetry (MIRD) calculation schema

12. Factors determining internal dose
Administered activity
Initial activity in the source organ and the length of stay in the organ, depending on biodistribution and physical decay
Energy emitted per decay
Absorbed fraction by the target organ, depending on distance, attenuation, and target organ volume and composition

13. Factors determining internal dose
Source and target organs

14. MIRD calculation schema
Mean absorbed dose
 D = ÃS orD/A0 = tS
Where t = Ã /A0
A0: administered activity. It is known.
à is activity accumulated in the source organ and t is the residence time. à or t depends on initial biodistribution, physical decay (lp), and biologic behavior (lb). It can be estimated by imaging at multiple times.

15. MIRD calculation schema (Medical Internal Radiation Dose)
S: dose to the target organ from unit cumulated activity in the source organ
S has been tabulated for many organs and also for many radiopharmaceuticals.
S depends on radiation energy per decay and absorbed fraction by the target organ f.
0 < f < 1, determined by photon energy and distance, attenuation, volume and composition of the target organ

16. Absorbed dose to individual organs
F18- Tc99m-
FDG(10 mCi) ECD(30 mCi) Tl (3 mCi)
(ethyl cysteinate dimer)
brain 17 mSv
kidneys
heart
ovaries
testes
Spleen
bladder
______________________________________________
EDE 8.6 mSv mSv mSv
ECD ethyl cysteinate dimer: CBF imaging
Tl: Thallous Chloride: coronary artery disease
FDG: cancer, neurological disease, myocardial disease

17. Effective dose of NM procedures

18. ACOB/GYN’s statement and regulations
“Women should be counseled that x-ray exposure from a single diagnostic procedure does not result in harmful fetal effects. Specifically, exposure to less than 50 mGy has not been associated with an increase in fetal anomalies or pregnancy loss.”
Regulatory dose limit for the fetus of a declared pregnant worker is 5 mSv during the pregnancy.

19. Absorbed dose to fetus early 1st end of 1st trimester trimester
_______________________________________
bone scan
(20 mCi 99mTc-MDP) 5 mSv mSv
WB PET scan
(15 mCi 18F-FDG) mSv mSv
thyroid scan
(0.2 mCi 123I) mSv mSv
all dose << 50 mSv
Up to about 12 weeks, the fetal thyroid does not take up iodine. After ~12 weeks, iodine concentrates in the fetal thyroid in amounts considerably greater than those of the maternal thyroid.

20. Absorbed dose to fetus
Iodine can cross the placenta but fetal thyroid does not cumulate iodine before 12 wk of gestation.
Mental retardation from radiation occurs primarily at 8 to 15 weeks of gestational period.
A large portion of radiation comes from mother’s bladder so hydration and frequent voiding may reduce the radiation.

21. Radiation protection U.S. Federal regulations (10CFR 19, 20, and 35)
ALARA: philosophy of radiation use whereby radiation dose is “as low as reasonably achievable”

22. Regulatory agencies Nuclear Regulatory Commission (NRC) FDA
To regulate the nation's civilian use of byproduct, source, and special nuclear materials to ensure adequate protection of public health and safety, to promote the common defense and security, and to protect the environment. The NRC's regulatory mission covers three main areas: reactor safety, radioactive materials used in medicine, industry and research, and nuclear waste management
FDA
To regulate radio-pharmaceuticals and NM devices

23. Regulatory agencies EPA
To regulate the radiation released to environment
DOT
To regulate the transportation of radioactive
material
Agreement States
To enter an effective regulatory discontinuance agreement with the NRC to regulate most types of radioactive material in accordance with the compatibility requirements of the NRC 

24. Agreement States
37 states have signed an agreement with the Nuclear Regulatory Commission stipulating that they will be the sole regulators, but will follow Federal guidelines. They may be more restrictive than these guidelines, but not less restrictive. In August, 2013, the NRC put the state of Georgia on probation due to multiple failures. The next review was set to be in January, The State passed the review.

25. Agreement States (2015)

26. Advisory bodies
International Commission on Radiological Protection (ICRP)
U.S. National Council on Radiation Protection and Measurements (NCRP)
International Atomic Energy Agency (IAEA)
Conference of Radiation Control Program Directors (CRCPD)

27. “Radiation badges” Minor likely to receive:
Anybody that may receive 1/10 of the annual occupational dose limit of 50 mSv needs to wear a radiation badge.
Minor likely to receive:
Annual external dose (DDE) > 1 mSv
LDE for eyes > 1.5 mSv
SDE for skin > 5 mSv
If the waiting area for injected patients is close to the secretary, she/he should wear a radiation badge.

28. How to wear a radiation badge?
For uniform radiation exposure, wear the badge on front of upper torso.
If particular body part is more exposed, wear the badge as close to this part as possible.
Wear the badge behind a lead apron (or at the collar outside the apron, GRU policy)
A person handling radionuclides must wear both whole body and ring badges.

29. How often are badges exchanged?
Every GRU
OSL = Optically Stimulated Luminescent Dosimeter
Monitoring is only required for external exposure. There is NO requirement to monitor the internal exposure.

30. Posting of badge reports
Film badge readings are routinely posted on bulletin board on a monthly basis. Employer is responsible for informing each employee on an annual basis of his cumulative radiation dose.

31. Occupational dose limits
For an adult worker < 50 mSv/yr
For an individual organ < 500 mSv/yr
For the eye lens < 150 mSv/yr
For fetus of a declared pregnant worker < 5 mSv/pregnancy
General public limits:
Dose < 1 mSv/yr
Exposure rate < 2 mR in any given hour

32. Declared pregnant radiation workers
A declared pregnancy is when an employee voluntarily informs the radiation safety office in writing of her pregnancy and estimated date of conception.
It is entirely the choice of the worker.
NRC dose limit is 5 mSv (10% of the annual occupational dose limit) to the fetus for the entire pregnancy (avoid substantial variation above a uniform monthly exposure rate).
An additional dosimeter badge should be worn at the level of the fetus.
If a worker chooses not to declare her pregnancy, the pregnancy dose limit does not apply.

33. Radiation dose to the hands
Typical dose received by hands without syringe shields is 5 to 10 mSv/hr/mCi when handling radionuclides.
For a radiation worker to reach the 500 mSv per year limit, she/he could spend hours handling a 10 mCi
syringe per year.
Syringe shields reduce the
dose by a factor of 3.

34. Radiation exposure rate around patient
Typical exposure rate at 1 m from the patient soon after injection:
Most radiopharmaceuticals:
1 mR/hr (maximum dose to public 1
mSv/yr)
18F-FDG: mR/hr
131I: 5 or 30 mR/hr for Graves or cancer dose respectively

35. Surveys for contamination
Survey with a GM meter must be performed at the end of each day in all areas where radioactive materials are prepared or administered.
The GM meter must be able to detect an exposure rate as low as 0.1 mR/h.
Wipe tests must be performed once a week where radioactive materials are prepared, administered or stored.
A record of the results should be kept.

36. Area surveys – daily
Using a GM meter, survey each room in which radioisotopes are used.
Record Model # & Serial # of the GM meter
Record actual reading; specify units (cpm or mR/hr)
Record background reading
Specify "action level" (criterion for immediate action if necessary)

37. Area wipe tests – weekly
An accurate area map must be drawn and, on a weekly basis, a dry wipes (filter paper or swab) are taken in each area where radionuclides are used.
The wipes are counted in a well counter that uses open energy window. Also background counts are obtained.
Results of the counting procedure are correlated with the area map. If greater than 6600 dpm/cm2, notify the RSO

38. Leak test of sealed sources
All sealed sources with half-life longer than 30 days (dose calibrator standards, well counter calibration sources, spot markers, etc.) must be wipe-tested before initial use and then every 6 months.
The results must be recorded in an appropriate logbook.
The test must be sensitive to µCi.

39. Labeling and storage of radionuclides
All containers, vials, syringes containing radioactive material should be
labeled properly
With radiation symbols and words such as CAUTION (or DANGER), RADIOACTIVE MATERIALS
Radionuclide
Quantity of radioactivity and time/date measured
Stored and shielded in secure area
Constantly monitored when not secured

40. Labeling and storage of radionuclides
A syringe shield needs to be labeled if it contains a syringe with radiopharmaceutical.
Alternatively, it may have a transparent portion to see the label.

41. Acceptable methods of waste disposal
Transfer to licensed person/company
Decay in storage
Release as effluents within authorized limits (generally unnecessary)

42. Radioactive sharps disposal
Use separate containers (e.g. sharps)
Seal when full and label date and longest half-life
3 S’s: Sealed, Shielded, Secure location
Before disposing, survey surfaces of container to make sure not higher than the background
Dispose of waste in appropriate containers (e.g. biohazard but no radiation symbol)

43. Radioactive package receipt
Must be inspected within 3 hours of receiving or, if after hours, within 3 hours of start of the next day
Visually inspect the package for the DOT radioactive material label, breakage, and leakage

44. DOT package labeling
White I
Yellow II
Yellow III
Surface exposure rate (mR/hr)
< 0.5
0.5-50
50-200
Transportation index
< 1
1-10
Transportation index (TI) is the exposure rate (mR/hr) measured at 1 meter from package.

45. DOT radioactive placard for the vehicle
Vehicles carrying packages bearing Yellow III labels are required to post the placard shown below on the outside of the vehicle. 7

46. Radioactive package receipt
Measure exposure rates 1 meter from package and at the surface
If normal, proceed to wipe test

47. Exposure rate at 1 meter

48. Exposure rate at surface

49. Radioactive package receipt
Wipe test
Wipe area is about 300 cm2 on all sides.
The counts should be less than 6600/min (22 dpm/cm2).
If normal, remove the packing slip and open the package.
Complete entry in receipt log
Store package in appropriate shielded area

50. Retention of records
Licensee shall maintain records including: …

51. ALARA
Efforts to reduce the radiation dose so long as the expenditure does not overweigh the gain
Decrease of exposure time for workers
Increase of distance (inverse square)
Shielding (e.g. lead pigs), signs and labels
Personnel protection and monitoring
ALARA levels at GRU
ALARA 1: 1.25 mSv in any given quarter
ALARA II: 3.75 mSv in any given quarter

52. Protection from external sources
Time around a radiation source
Distance from a radiation source
Shield for syringes, vials and dose calibrators, but usually not for walls

53. Photon intensity: inverse square law
Inverse square law used for unshielded source, particularly useful in PET
I = I0/d2
Exposure rate (R/hr) = GA/d2
G: exposure rate constant for a point source (Rcm2/(mCihr))
A: source activity, d: distance from source

54. 10 mCi F-18 radiation dose rate
Distance Dose rate w/o lead w 1/8” lead
0.5 m mrad/hr mrad/hr
1.0 m mrad/hr 3.5 mrad/hr
1.5 m mrad/hr 1.6 mrad/hr
2.0 m mrad/hr mrad/hr
2.5 m mrad/hr mrad/hr
3.0 m mrad/hr mrad/hr
3.5 m mrad/hr mrad/hr
4.0 m mrad/hr mrad/hr
30% increase in distance better than 1/8” lead shield

55. Photon intensity: exponential attenuation
Exponential attenuation in a medium
I = I0 exp(-md)
Reducing radiation using lead shield

56. Prevention against ingestion/absorption/inhalation of radioactivity
No eating, drinking and applying cosmetics in restricted areas
Wearing lab coats and gloves
Washing hands after handling radioactivity
Working with radioactive gases under a ventilated fume hood

57. What is wrong?
No gloves, no syringe shield, no label, not on counter with lead glass and absorber

58. What is wrong?
No lab coat, no gloves, no ring badge, no syringe shield, no label, no absorber under the injection spot, too happy perhaps?

59. Reportable medical events
Diagnostic events resulting in a dose that is
Greater than 50 mSv effective dose, or
Greater than 500 mSv dose equivalent to any organ, or
Greater than 500 mSv shallow dose equivalent to skin
Therapeutic events: administered dose exceeds 20% of prescribed dose

60. Reportable medical events
Dose equivalent to an embryo/fetus is higher than 50 mSv, unless the dose is approved in advance by the AU.
Dose to a nursing child is higher than 50 mSv or permanent damage to an organ or physiologic system of the child.
Events of patient intervention (intentional or unintentional action, e.g. removing treatment device) in which the dose may cause permanent damage

61. Reportable medical events
Must notify NRC/state, referring physician and patient in writing, giving pertinent details and plans for preventing recurrence
Mainly for radiotherapy not imaging
Agent EDE Highest organ dose
FDG (10 mCi) mSv 59 mSv
Tc-mibi (20 mCi) mSv 29 mSv
Tl (2 mCi) mSv 46 mSv

62. Recordable but not reportable events
Event resulting in a dose below the NRC limits. It may caused by
Administered dose falls 10% outside the prescribed dose range, or
Wrong patient, or
Wrong radiopharmaceutical, or
Wrong route of administration
Need to be recorded locally and kept for 10 years

63. Recordable but not reportable events
E.g. 10 mCi of In-111 octreotide is 66.7% more than the usually prescribed dose of 6 mCi. This is a recordable event for the hospital and nuclear medicine department but does not meet the NRC definition of medical event.

64. What is major spill? Activity released at location or on people
100 mCi Tc-99m or Tl-201
10 mCi Ga-67 or In-111
1 mCi I-131
Radiation safety officer must be present.
Focus on containment, shielding, and decontaminating individuals

65. What to do with a major spill?
Notify all persons in the area of spill
Prevent spread of contamination
Cover spill with disposable, absorbable paper
Remove contaminated clothing
Shield radioactivity if possible
Room sealed off
Report incident to RSO immediately
RSO directs further response.

66. What to do with a minor spill?
Notify all persons in the area of spill
Prevent spread of contamination
Cover spill with disposable, absorbable paper
Remove contaminated clothing
Clean up spill with disposable, absorbable paper
Survey the area until the exposure rate is lower than twice background level
Personnel monitored (hands, shoes, clothing)
Report incident to radiation safety officer

67. What is wrong?
The hot lab door is wide open.