The Basics of Radiation Safety

Transcription

1 Cardiac Imaging Symposium 2013 UNIVERSITY OF OTTAWA HEART INSTITUTE The Basics of Radiation Safety Leah Shuparski-Miller Medical Health Physicist Radiation Safety & Emergency Preparedness Department The Ottawa Hospital

2 Training Objectives Understand basic radiation concepts Discuss radiation protection in a patient context Discuss radiation protection in an occupational context 2

3 Quiz! Have you received radiation safety training before? A.No, never B.Yes, in my medical school undergrad courses or electives C.Yes, in a research lab context D.Yes, at this institution 3

4 Radiation: The transmission of energy through space in the form of waves or streams of particles causes chemical changes causes NO chemical changes Eric J Hall, Professor of Radiology, Columbia University, New York; Radiation and Life

5 LASER Warning Sign non-ionizing radiation

6 Ionizing Radiation Radiation that has sufficient energy to ionize (remove electrons) from an atom. 6

7 X-Ray Production Electron Target Nucleus Tungsten X-Ray Cathode (-) X-Ray tube Anode (+) X-Rays 7

8 Radioactive Decay Beta Particle Tritium (or Hydrogen-3) Atomic Number = 1 Mass Number = 3 Helium-3 Atomic Number = 2 Mass Number = 3 8

9 Forms of Radioactive Decay Alpha decay: too heavy! An alpha particle is made up of two protons and two neutrons. Occurs when the nucleus of an atom spontaneously ejects an alpha particle Beta minus decay: too many neutrons! Neutron changes into a proton, nucleus emits a negative beta particle (electron) and an antineutrino. Beta plus decay: too many protons! Proton changes into neutron, emits positive electron. Positive electron interacts with an electron, and send off two gammas at exactly the same time in exactly opposite directions. Gamma decay: The nucleus has excess energy that will be released in the form of a gamma ray. Useful for imaging 9

10 Population Exposure Data from NCRP 160 (US) 10

11 Natural Background Radiation Natural radiation that the average person receives every year Radon 74% Space Background 10% Internal Emitters 10% Terrestrial Background 6% Average natural background in North America~ 3 msv/yr 11

12 Routes of Exposure External Radiation Field -Whole Body -Skin 12

13 Natural Radioactivity in Food Food 40 K 226 Ra Bq/kg Bq/kg Banana 130, Brazil Nuts 207,200 37, ,000 Carrot 125, White Potatoes 125, Beer 14, Red Meat 111, Lima Bean Raw 171, Drinking water

14 Internal Routes of Exposure Inhalation Ingestion/injection Absorption through intact skin Absorption through wound 14

15 Units for Activity Amount of decays per unit time. S.I. System: The Becquerel 1 Bq = 1 decay per second Non-S.I. System: The Curie 1 Ci = 3.7x10 10 decays per second Typical Administered Doses FDG Scan F-18 Cardiac Stress Tc- 99m Thyroid Ablation I mci 32 mci 100 mci 500 MBq 1200 MBq 3700 MBq 1 mci=37mbq

16 Radioactive decay Half-life Half-lives of Typical Medical Isotopes F min Tc-99m Tl hours 73 hours I days 16

17 Quiz! The hot lab received 16 mci of F18 (half-life: 2 hrs). The scan is delayed by 4 hours. How much activity is left? A.8 mci B.4 mci C.12 mci D.10 mci 17

18 Radiation Dose Gy Gray absorbed dose Joule/kg Energy per mass x tissue weighting factor x radiation weighting factor Sv Sievert effective dose Gy x weighting factors Biological effect of the radiation Typical scale for medical procedures and occupational exposure: millisievert (msv) = 10-3 Sv

19 Quiz! Which organ or tissue has the highest weighting factor (ie which is considered the most radiosensitive)? A.Thyroid B.Gonads C.Lungs D.Skin E.Esophagus 19

20 Effective Dose Weighting Factors Tissue w T Σw T Red Bone Marrow, Lungs, Stomach, Colon, Breast, Remainder Gonads Bladder, Esophagus, Liver, Thyroid Bone surface, brain, salivary glands, skin Table 3, ICRP 103 The 2007 Recommendations of the ICRP 20

21 How does it affect the body? Interactions with DNA Direct Effect Indirect Effect How particle radiation induces DNA damage 21

22 Radiation Effects Stochastic Deterministic theoretical measured cancer risk-cumulative? skin reddening 3-5 Sv linear-no-threshold (LNT) cataracts 0.5 Sv hypothesis cancer therapy 1-10 Gy

23 Patient Radiation Protection Justification: Radiation does more good than harm in medicine Specified procedure with specific objective Application of procedure to specific patient Optimization: lowest dose possible for the procedure (no dose limits) 23

24 Explaining Risk Emphasis on risk of NOT having procedure: highlight the medical benefits Comparison to natural background Comparison to other risks in life 24

25 Comparison to Natural Background Relate the dose received from the procedure to the number of days lived in Ontario. For example Rest Test (Tc-99m) ~ 3 msv is received by living in Ontario for 1 year. 25

26 AAPM Position Statement on Radiation Risks from Medical Imaging Imaging procedures should be appropriate and conducted at the lowest radiation dose discussion of risks should be accompanied by the acknowledgement of the benefits of the procedures. Risks at effective dose below 50 msv (single procedure) or 100 msv for multiple procedures over short time periods are too low to be detectable and may be nonexistent. Predictions of hypothetical cancer incidence and deaths in patient populations exposed to such low doses are highly speculative and should be discouraged..

27 Quiz! Which procedure do you think has the highest radiation dose, on average? A.PET scan (FDG) B.Chest CT C.Rest+ Stress (Tl-201) D.Coronary Angiography 27

28 Average Patient Doses 0.02 msv Chest X-Ray 2.8 msv* Rest Tc-99m 7.7 msv* Stress Tc-99m 20.2 msv* Rest/Stress Tl msv* FDG PET 8.0 msv** Chest CT 9.1 msv*** Coronary Angiography 10 msv ** CT Abdo + Pelvis *ICRP53 addendum 2 (ICRP80) 2000 **NRPB-W4 (ISBN ). NRPB. Didcot ***Patient Radiation Doses in Interventional Cardiology Procedures Current Cardiology Reviews, 2009, Vol. 5, No. 1 28

29 ICRP 103 Risk Estimates, 2007 Numerical estimates assume a linear relationship between risk and dose. 4% excess fatal cancers per Sv in adults (4 extra cancers in per msv) Data comes from: Animal studies Hiroshima/Nagasaki Chernobyl Medical, occupational, environmental exposures 29

30 Putting Risk in Perspective 25% of Canadians will die of cancer * 50 msv is considered to increase the risk of fatal cancer from 25% to 25.2% in adults *Canadian Cancer Society s Advisory Committee on Cancer Statistics. Canadian Cancer Statistics Toronto, ON: Canadian Cancer Society;

31 Radiation at Higher Doses Tissue reactions 2 Gy early transient erythema (2-24 h onset) 3 Gy temporary epilation (3 wk onset) 18 Gy moist desquamation Whole body doses 0.75 Sv (750 msv) some detectable changes in blood <1 Sv (1000 msv) no immediate harmful effects LD50 is 4.5 Sv 31

32 Optimization Nuclear Medicine & PET Correct dose: usually activity/kg for imaging Cath/EP Use last image hold instead of re-fluoro Source: as far away as possible from bed Image receptor: as close as possible to pt Decrease fluoro frame rate if possible 32

33 Occupational Exposure Justification Optimization Dose Limits 33

34 Nuclear Energy Worker (NEW) or X-Ray Worker (XRW) Nuclear Energy Worker means a person who is required, in the course of the person s business or occupation in connection with a nuclear substance or nuclear facility, to perform duties in such circumstances that there is a reasonable probability that the person may receive a dose of radiation that is greater than the prescribed annual limit for the general public (1 msv). (Nuclear Safety and Control Act) X-Ray Worker is defined as: a worker who, as a necessary part of the worker s employment, may be exposed to x-rays and may receive a dose equivalent in excess of the annual limits for non-xray workers as defined (1 msv). (in the Regulations 861, Section 1 of the Occupational Health & Safety Act). 34

35 Other RP Considerations Sources of Stray Radiation: X-Ray Tube Leakage Scatter from objects exposed to the X-Ray beam (including the patient/subject) Example of scatter:

36 Stray Radiation: Scatter The number of scattered X-Rays increases when: Patient/subject skin exposure rate increases Patient/subject entrance skin area (field size) increases Beam energy (kvp) increases Scatter intensity is higher on the entrance side (forward scatter is heavily attenuated)

37 Basic Radiation Protection Principles Time Distance Shielding To Decrease Someone s DOSE

38 Time The shorter the period of time that one is exposed to radiation, the lower the dose that will be absorbed. Dose = Time (hr) x Dose Rate (usv/hr) Shielding e.g. lead aprons, mobile/portable shielding, bismuth/tungsten shielding; concrete Radiation Type Tc-99m (140 kev) Lead required to reduce radiation dose to 10% of initial value 1 mm F-18 (511 kev) 16 mm 130 kvp X-Ray (average energy 45 kev) mm

39 Stopping ionizing radiation Concrete (1m) Lead (2 in) Plexiglass 32 P, 90 Sr Tc99m, Tl201, F18 Alpha Beta Gamma (X-Ray) Radiation Therapy 39

40 40

41 Type of Eye Shielding Ceilingsuspended shields Leaded goggles Drape shield Lead curtains Eye Dose Rate Reductions >1000 x * Type of Protection Personal (head) 2-3 x in practice ** Personal (eyes) 5-10 x * 12 x eyes * 26 x thyroid * Not available All in the room All in the room Recommended for Type of Costs All procedures *,**, + One-time When ceilingsuspended shields cannot be used +,** Procedures where operator s hands must be near the radiation field (dialysis fistulas/grafts, biliary and genitourinary) + All procedures** Ongoing (every few years) New drape required for each procedure One-time

42 Distance The further you are away from a radiation source, the less radiation you will receive (not linear) Gray (Gy) j/kg Sievert (Sv) j/kg (PA imaging)

43 Quiz! During LAT imaging, which of the two positions is preferable? A.On the source side B.On the detector side 43

44 Lateral Projections B A

45 Lateral Projections B A

46 Regulations Annual Dose Limits Provincial Regulations Federal Regulations X-Ray Workers Other Workers Nuclear Energy Workers Public Whole body 50 msv 5 msv 20 msv 1 msv Lens of Eye * Extremity (skin or hands and feet) Pregnant women 150 msv (20 msv) 50 msv 150 msv (20 msv) 15 msv 500 msv 50 msv 500 msv 50 msv 5 msv 1 msv 4 msv 1 msv ALARA

47 Eye Dose Limits ICRP International Commission Radiological Protection Old ICRP Eye Dose Limit Recommendation New ICRP Eye Dose Limit Recommendation 150 mgy/y Longer follow up at lower doses Better sensitivity in detecting lens opacities and cataracts 20 mgy/y averaged over 5 years, with no one year exceeding 50 mgy

48 Obligation of Pregnant NEW and XRW Congratulations! Complete and sign a Declaration of Pregnancy Notify your supervisor Why? Can t keep your dose below pregnant worker limits or put in place accommodations if we don t know you re expecting 48

49 Monitoring of Workers Electronic Personal Dosimeter Not a choice. Strictly Regulated!

50 Personal Dosimeters In X-Ray, whole body and extremity (head/collar) are measured During RED / BLUE quarters: RED: Head/collar (outside your lead, at neck) BLUE: Whole body (behind your lead) During WHITE / GREEN quarters: GREEN: Head/collar (outside your lead, at neck) WHITE: Whole body (behind your lead)

51 2012 Whole Body Doses TOH 51

52 2012 Extremity Doses TOH 52

53 ALARA As Low As Reasonably Achievable Justification : risk vs benefit Optimization Dose limits Low radiation dose High radiation dose Where in this region should we be? Poor image quality Good image quality 53

54 Questions? Concerns? or 54