Nuclear Medicine Physics - PowerPoint Presentation

Slide1

Nuclear Medicine Physics

Jerry Allison, Ph.D.Department of Radiology & ImagingMedical College of GeorgiaAugusta University

Radiation Protection in Nuclear MedicineSlide2

A note of thanks to Z. J. Cao, Ph.D.Medical College of GeorgiaAnd

Sameer Tipnis, Ph.D.G. Donald Frey, Ph.D.Medical University of South CarolinaforSharing nuclear m

edicine presentation contentSlide3

Information for Patients Administered Radioactive Iodine (I-131

)

https

://www.nrc.gov/materials/miau/patient-release.htmlSlide4

4Radiation exposure of the publicSlide5

5Sources 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, c

osmic rays from the sky, and internal radiation from 40K, 14C and 3HFallout

from nuclear power stations and consumer products: 0.46 mSv/person/yr (10%) Medical: 0.54 mSv/person/yr (12%)Slide6

6Sources 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 0.54 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: 1982

2006

NM

6 M

18

M (3% of

all)

CT

3

M

67

M (12% of all

)Slide7

7Radiation dose effectsSlide8

8Stochastic and non-stochastic effectsS

tochastic: 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. Slide9

9Models 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 Slide10

10Models of low-dose response

dose

1 Sv/yr

damage

benefit

linear

hormesis

linear+quadric

high dose dataSlide11

11 Internal dosimetryFactors determining internal dose

Medical internal radiation dosimetry (MIRD) calculation schemaSlide12

12Factors determining internal dose

Administered activity Initial activity in the source organ and the length of stay in the organ, depending on biodistribution and physical decayE

nergy emitted per decay Absorbed fraction by the target organ, depending on distance, attenuation, and target organ volume

and compositionSlide13

13Factors determining internal doseSource and target organsSlide14

14MIRD calculation schema

Mean absorbed dose  D = ÃS orD/A0 = tS

Where t = Ã /A0

A0: administered activity. It is known.

Ã

is

activity accumulated in the source

organ and

t

is the r

esidence time

.

Ã

or

t

depends on

initial

biodistribution,

physical decay

(

l

p

), and biol

ogic behavior

(

l

b

). It can be estimated by imaging at multiple times.

Slide15

15MIRD calculation schema(Medical Internal Radiation Dose)

S: dose to the target organ from unit cumulated activity in the source organS 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 Slide16

16Absorbed dose to individual organs

F18- Tc99m- FDG(

10 mCi) ECD(30 mCi

) Tl (3 mCi)

(ethyl

cysteinate

dimer)

brain

1

7

mSv

0

.

4

6

.

6

kidneys

7.8

5

.

8

51

heart 2

5

1

.

3

3

ovaries

4.1

5

.

8

11testes 4

.1

2

.

6

22

Spleen

5.6

1

.

5

2

bladder

27

54

5

.

7

______________________________________________

EDE

8.6

mSv

8

.

4

mSv

18

mSv

Slide17

Effective dose of NM procedures 17Slide18

18ACOB/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.Slide19

19Absorbed dose to fetus

early 1st end of 1st trimester trimester

_______________________________________bone scan

(20 mCi 99mTc-MDP) 5 mSv 4

mSv

W

B

PET

scan

(15 mCi

18

F-FDG)

15

mSv

10

mSv

t

hyroid scan

(0.2 mCi

123

I)

0.2

mSv

0.1

mSv

all dose << 50 mSvSlide20

20Absorbed dose to fetusIodine

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. Slide21

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

21Slide22

22Regulatory agencies Nuclear Regulatory Commission

(NRC) 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 managementFDA To regulate radio-pharmaceuticals and NM devicesSlide23

23Regulatory agenciesEPA

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 

Slide24

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, 2014. The State passed the review.

24Slide25

Agreement States (2015) https://scp.nrc.gov/rulemaking.html25Slide26

26Advisory 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)Slide27

“Radiation badges”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 mSvIf the waiting area for injected patients is close to the secretary, she/he should wear a radiation badge.Slide28

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.28Slide29

How often are badges exchanged?

Every month @ GRUOSL = Optically Stimulated Luminescent DosimeterMonitoring is only required for external exposure. There is NO requirement to monitor the internal exposure.Slide30

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. Slide31

31Occupational dose limits

Occupational dose limits: For an adult worker < 50 mSv/yr For an individual

organ < 500 mSv/yr For the e

ye lens < 150 mSv/yr For fetus of a

declared p

regnant

worker

<

5

mSv

/pregnancy

G

eneral public limits:

Dose

<

1

mSv

/yr

Exposure rate

< 2 m

R in any given

hourSlide32

Declared pregnant radiation workersA 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.Slide33

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 5-10 hours handling a 10 mCi syringe per year.

Syringe shields reduce the dose by a factor of 3.Slide34

Radiation exposure rate around patientTypical 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: 5 - 30 mR/hr131I: 5 or 30 mR/hr for Graves or cancer dose respectivelySlide35

Surveys for contaminationSurvey 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.Slide36

Area surveys – daily Using

a GM meter, survey each room in which radioisotopes are used.Record Model # & Serial # of the GM meterRecord actual reading; specify units (cpm or mR/hr)Record background readingSpecify "action level" (criterion for immediate action if necessary)Slide37

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 RSOSlide38

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 0.005

µCi.Slide39

Labeling and storage of radionuclidesAll containers, vials, syringes containing radioactive material should be labeled properlyWith radiation symbols and

words such as CAUTION (or DANGER), RADIOACTIVE MATERIALSRadionuclideQuantity of radioactivity and time/date measured Stored and shielded in secure area Constantly monitored when not securedSlide40

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.Slide41

Acceptable methods of waste disposal Transfer to licensed person/company

Decay in storage Release as effluents within authorized limits (generally unnecessary)Slide42

Radioactive sharps disposalUse separate containers (e.g. sharps)

Seal when full and label date and longest half-life3 S’s: Sealed, Shielded, Secure locationBefore disposing, survey surfaces of container to make sure not higher than the backgroundDispose of waste in appropriate containers (e.g. biohazard but no radiation symbol)Slide43

Radioactive package receiptMust 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 leakageSlide44

DOT package labelingTransportation index (TI) is the exposure rate (mR/hr) measured at 1 meter from package.

White I

Yellow II

Yellow III

Surface exposure rate (mR/hr)

< 0.5

0.5-50

50-200

Transportation index

0

< 1

1-10Slide45

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

7Slide46

Radioactive package receipt Measure exposure rates 1 meter from package and at the surfaceIf normal, proceed to wipe test

46Slide47

E

xposure rate at 1 meter Slide48

E

xposure rate at surfaceSlide49

Radioactive package receiptWipe 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 logStore package in appropriate shielded area49Slide50

Retention of records

20.2102 - Licensee shall maintain records including:…Slide51

51ALARA

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 monitoringALARA levels at GRUALARA 1: 1.25 mSv in any given quarterALARA II: 3.75 mSv in any given

quarterSlide52

52Protection from external sources

Time around a radiation sourceDistance from a radiation sourceShield for syringes, vials and dose calibrators, but usually not for wallsSlide53

53Photon intensity: inverse square law

Inverse square law used for unshielded source, particularly useful in PET I = I0/d2Exposure 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 Slide54

5410 mCi F-18 radiation dose rate

Distance Dose rate w/o lead w 1/8” lead 0.5 m 22.6 mrad/hr 13.6 mrad/hr 1.0 m 6.3 mrad/hr 3.5 mrad/hr 1.5 m 3.0 mrad/hr 1.6 mrad/hr 2.0 m 1.4 mrad/hr 0.90 mrad/hr 2.5 m 0.93 mrad/hr 0.54 mrad/hr 3.0 m 0.62 mrad/hr 0.41 mrad/hr

3.5 m 0.48 mrad/hr 0.29 mrad/hr 4.0 m 0.39 mrad/hr 0.23 mrad/hr30% increase in distance better than 1/8

” lead shieldSlide55

55Photon intensity: exponential attenuation

Exponential attenuation in a medium I = I0 exp(-md)Reducing radiation using lead shieldSlide56

56Prevention against ingestion/absorption/inhalation of radioactivity

No eating, drinking and applying cosmetics in restricted areasWearing lab coats and glovesWashing hands after handling radioactivityWorking with radioactive gases under a ventilated fume hoodSlide57

What is wrong?

No gloves, no syringe shield, no label, not on counter with lead glass and absorberSlide58

What is wrong?58

No lab coat, no gloves, no ring badge, no syringe shield, no label, no absorber under the injection spot, too happy perhaps?Slide59

Reportable medical events Diagnostic events resulting in a dose that isGreater than 50 mSv effective dose, or Greater than 500 mSv dose equivalent to any

organ, orGreater than 500 mSv shallow dose equivalent to skin Therapeutic events: administered dose exceeds 20% of prescribed doseSlide60

Reportable medical eventsDose 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 damageSlide61

61Reportable medical eventsMust notify NRC/state, referring physician and patient in writing, giving pertinent details and

plans for preventing recurrenceMainly for radiotherapy not imaging Agent EDE Highest organ dose FDG (10 mCi) 7.0 mSv 59 mSvTc-mibi (20 mCi) 7.0 mSv 29 mSvTl (2 mCi) 12 mSv 46 mSvSlide62

Recordable but not reportable eventsEvent 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, orWrong route of administrationNeed to be recorded locally and kept for 10 years 62Slide63

Recordable but not reportable eventsE.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 m

edicine department but does not meet the NRC definition of medical event.Slide64

What is major spill?Activity released at location or on people100 mCi Tc-99m or Tl-20110 mCi Ga-67 or In-111

1 mCi I-131Radiation safety officer must be present.Focus on containment, shielding, and decontaminating individuals Slide65

What to do with a major spill?Notify all persons in the area of spillPrevent spread of contaminationCover spill with disposable, absorbable paperRemove contaminated clothing

Shield radioactivity if possibleRoom sealed offReport incident to RSO immediatelyRSO directs further response.65Slide66

What to do with a minor spill?Notify all persons in the area of spillPrevent spread of contaminationCover spill with disposable, absorbable paper

Remove contaminated clothingClean up spill with disposable, absorbable paperSurvey the area until the exposure rate is lower than twice background levelPersonnel monitored (hands, shoes, clothing) Report incident to radiation safety officerSlide67

What is wrong?

The hot lab door is wide open.