The Center for Radiation Protection Knowledge: The Who, What and Why

Transcription

1 The Center for Radiation Protection Knowledge: The Who, What and Why Nolan E. Hertel Georgia Institute of Technology Center for Radiation Protection Knowledge ORNL is managed by UT-Battelle for the US Department of Energy 1

2 2 About the Center for Radiation Protection Knowledge at Oak Ridge National Laboratory

3 Oak Ridge National Laboratory 3

4 Director 4 Center for Radiation Protection Knowledge (CRPK)

5 Center for Radiation Protection Knowledge Top: Nolan Hertel (JFA, Georgia Institute of Technology) Keith Eckerman (Emeritus) Rich Leggett (R&D Scientist) Clay Easterly (Consultant) Richard Ward (Consultant) Middle: Michael Bellamy (ORNL, R&D Engineer) Shaheen Dewji (ORNL, R&D Engineer) Derek Jokisch (JFA, Francis Marion U) Bottom: Ken Veinot (Consultant) Pat Scofield (ORNL) Scott Schwahn (ORNL) 5

6 ORNL Dosimetry Research Program: The Legacy ORNL Dosimetry Research Program was started in the 1950s by K. Z. Morgan, Director of ORNL s Health Physics Division Morgan early recipient of the Swedish Royal Academy Gold Medal for Radiation Protection. From , program was led by Keith Eckerman Recipient of the Swedish Royal Academy Gold Medal for Radiation Protection (2012) Now part of ORNL s Environmental Sciences Division Former group members read like a Who s Who in Radiation Protection Dosimetry 6

7 ORNL Dosimetry Research Program: The Legacy Provided the national and international scientific communities with models and data To estimate doses from exposure to radionuclides To establish exposure guidelines for radionuclides These models generally have become international standards A center for archival and computer implementation of biokinetic and dosimetric models 7

8 Center for Radiation Protection Knowledge ( Established at ORNL per MOU 2010 Original Signers: DOE, DoD, EPA, NRC, and OSHA MOU renewed 2015: 2015 DHHS added 2016 DHS added Maintaining/Preserving U.S. expertise and leadership Development/Application of Radiation Dosimetry and Risk Assessment Methodologies/Models Ensure the best scientifically available knowledge in regulatory processes and decision making 8

9 CRPK Dose Coefficients: Global Impact International Organizations: Software: CAP88 IMBA COMPLY DCFPAK 9 Turbo FRMAC RASCAL RESRAD EPA-PRGS International Commission on Radiological Protection (ICRP) International Commission on Radiation Units and Measurements (ICRU) Domestic Organizations: Environmental Protection Agency (EPA): Federal Guidance Reports (FGR) Nuclear Regulatory Commission: Code of Federal Regulations (CFR) National Council on Radiation Protection and Measurements (NCRP) and more!

10 Center for Radiation Protection Knowledge CRPK Objectives 1. Maintain state-of-the-art biokinetic and dosimetric methodologies 2. Make methodologies available to stakeholders in Federal agencies and to the scientific community 3. Provide technical assistance to stakeholders 4. Provide technical analyses and documentation to support Federal Guidance Technical Reports 5. Provide training material and courses for stakeholders 10

11 Dose Coefficients: What are they? Where do I find them? [How do I use them?] 11

12 Estimation of Radiation Doses to Humans Dosimetric Models (radiation transport) Internal Dosimetry Compute dose in target organs due to radiation emitted from source organs of the body. External Dosimetry - Dosimetric models are also used to estimate tissue/organ doses from external sources of ionizing radiation. Biokinetic Models - Time-dependent distribution, retention, and excretion of radionuclides entering the body through inhalation, ingestion, wounds, or injection. 12

13 Inhalation and Ingestion of Radionuclides 13 Biological (biokinetic) Breathing and ingestion rates Excretion Time varying distribution Retention Dose per intake (Sv/Bq) Physical (dosimetric) Radiological Half-life Types and energies of emitted radiation Radiation interaction cross-sections Tissue mass, composition and density Dimensions of reference humans Dose per Concentration (Sv/s per Bq/m 3 )

14 Reference Data Incorporated 14 Reproduced from: Lee, C. (2015). Dosimetry Tools for Medical Radiation Studies. Radiation Epidemiology & Dosimetry Course.

15 15 ORNL Developed Biokinetic Models Basic physiological system models For example, blood circulation or transit of material through the gastrointestinal transit Systemic, alimentary, respiratory Many applied for a variety of purposes Nutrition studies Assessment of chemical toxicity Radiation dose reconstruction for epidemiological studies Forensic tool - ORNL s model used to find quantity of Po-210 used in poisoning of a former Russian spy in the UK Dynamic Blood Flow Model (A Generic Physiological Systems)

16 Pu, Am, Cm Biokinetics ICRP OIR Part 2 (2016*) Recycling model ICRP 72 (1995) ICRP 30 (1979) 16

17 Dose Coefficients: What are they? Where do I find them? How do I use them? 17

18 18 Radiological Toolbox 3.0.0

19 Radiological Toolbox User's Guide (NUREG/CR-7166, ORNL/TM-2013/16) 19 Provides electronic access to the vast and varied data that underlies the field of radiation protection. The initial motivation was to serve the needs of the health physicist away from his office, e.g., NRC inspectors. Earlier releases were widely used and accepted around the world by not only practicing health physicist but also those within educational programs. Version Updated to run on Windows 7 and 8 and on 32- and 64- bit machines. Nuclear decay data updated and now includes thermal neutron capture cross sections and cancer risk coefficients

20 20 Time for a smart phone version?

21 RadToolbox Available (registration required) on U.S. Nuclear Regulatory Commission Radiation Protection and Computer Code Maintenance Program (RAMP) NRC RAMP Website RAMP Website ORNL inquiry: 21

22 22 Dose Coefficient File Package (DCFPAK)

23 Dose Coefficient File Package (DCFPAK) The software and data package DCFPAK (Dose Coefficient File Package) provides electronic access to Nuclear decay data Dose and risk coefficients for exposure to radionuclides Eight versions of DCFPAK from 1996 through 2008 Current version DCFPAK 3.0 has an expanded set of radionuclides addressed in the inhalation and ingestion scenarios DCFPAK 4.0 is due for release shortly 23

24 DCFPAK A joint project between Oak Ridge, Argonne, and Sandia National Laboratories to resolve key issues with DCFPAK Transform DCFPAK data into a common format Provide a common DCFPAK version across the user community Provide a common point of access to DCFPAK Solution was to develop a DCFPAK Website. 24

25 DCFPAC Users (a sampling of users) National Incident Response Center s Turbo FRMAC software. The implements the science and methodologies utilized by the Federal Radiological Monitoring and Assessment Center (FRMAC). Utilized in the event of release of radioactive material to guide and govern the response of the Federal, State, Local, and Tribal governments. ANL/DOE RESRAD codes US Nuclear Regulatory Commission RASCAL (Radiological Assessment System for Consequence Analysis) code HotSpot 25

26 Dose Coefficients: What are they? Where do I find them? [How do I use them?] 26

27 Support of EPA Federal Guidance and US NRC Codes of Federal Regulation Provide US federal agencies with the technical information needed to implement radiation protection programs for workers and the public. Federal Guidance Report 15 revision of FGR12 (External Exposure to Radionuclides in Air, Water, and Soil) Radionuclides using ICRP Publication 103 dose quantity recommendations and ICRP Publication 107 Decay Data Age-dependent - Newborn, 1, 5, 10, 15 and Adult (Male and Female) Stylized Phantoms Dose coefficients exposure pathways Submersion in a contaminated atmosphere Exposure to contamination on or below the ground surface Immersion in contaminated water Effective doses and 29 sex-averaged, age-dependent organ equivalent doses by age

28 2-Step Calculation with MCNP Compute photon incidence data on a coupling cylinder 2. Insert different phantoms in the cylinder and run the incidence data to compute the organ absorbed doses.

29 Ground Plane 29

30 30 Infinite Soil Uniformly Contaminated

31 Air Submersion 31

32 Water Immersion 32

33 Support of EPA Federal Guidance and US NRC Codes of Federal Regulation Federal Guidance Report 16 revision of FGR13 (Cancer Risk Coefficients for Environmental Exposure to Radionuclides) Estimating risks due to internal and external radionuclide exposures. FGR 13: ~800 radionuclides. FGR 16: 1252 radionuclides Both mortality and incidence risk coefficients are tabulated for inhalation, food and water ingestion, submersion in air and exposure to uniform soil concentrations. The age-averaged coefficients consider age-specific intake rates, dose modeling, and risk modeling. Overlap with US NRC 10 CFR20 and 50 PART 20 Standards for Protection Against Radiation PART 50 Domestic Licensing of Production and Utilization Facilities 33

34 34 Computational Framework Internal Dose Coefficients

35 Revision of FGR 13: Cancer Risk Coefficients for Environmental Exposure to Radionuclides 35 Methods and data for estimating risks due to both internal and external radionuclide exposures. Coefficients for assessing cancer risks from environmental exposure to about 800 radionuclides. FGR 16 will have 1252 radionuclides Both mortality and incidence risk coefficients are tabulated for inhalation, food and water ingestion, submersion in air and exposure to uniform soil concentrations. The age-averaged coefficients consider age-specific intake rates, dose modeling, and risk modeling. The information presented in this report is for use in assessing risks from radionuclide exposure in a variety of applications ranging from environmental impact analyses of specific sites to the general analyses that support rulemaking.

36 DCAL (Dose and risk coefficient software) DCAL is a comprehensive software system for the calculation of tissue dose and subsequent health risk from intakes of radionuclides or exposure to radionuclides present in environmental media. 36 DCAL was developed for the U.S. Environmental Protection Agency Now in revision

37 An Example Doses to Members of the Public from 131 I Patient Release using the PIMAL Phantom 37

38 Motivation Work funded by United States Nuclear Regulatory Commission Part of a review of its policy and guidance on releasing patients from treatment facilities following administration of diagnostic or therapeutic doses of iodine. 38

39 Objective Extensive data on measured doses to medical staff and to family members but, for obvious reasons, none on dose to fellow passengers and workers at hotels and nursing homes, which are places that may be frequented by recently released patients. Calculate external dose resulting from released patients to members of the public in various exposure scenarios: 1. Public Transportation 2. Nursing Home 3. Hotel 39

40 Patient Cases Considered Thyroid Cancer Normal DTC - 5% uptake 30% peak content with no decay, ~27% for I-131 Hyperthyroid 80% peak content 40

41 Exposure Cases Considered I) Public Transportation Face-to-Face Standing (10cm Separation) 2. Patient Seated in Front of Person 3. Patient Seated Behind Person 4. Patient Seated Side-by-Side 5. Patient Standing beside Seated Person 6. Patient Seated beside Standing Person II) Nursing Home 1. Caregiver Seated 30cm from Patient Bed 2. Patient 250cm from Nursing Home Roommate III) Hotel Room 1. Back-to-Back Seated in Bed in Adjacent Rooms 2. Back-to-Back Lying in Bed in Adjacent Rooms

42 Methodology Model the patient and member of the public Model movement of 131 I in the patient s body as a function of time Retention per Bq Uptake 1.20E E E E E E-01 Normal Thyroid (27%) DTC (5%) Hyperthyroid (80%) 0.00E Time (Hours) Calculate the dose rate to the member of the public as a function of time Integrate dose rates to calculate total dose for the exposure scenarios 42

43 Methodology Monte Carlo Simulation Adult mathematical hermaphrodite phantom PIMAL (Phantom with Movable Arms and Legs) developed at ORNL. ICRP 89 tissue compositions and densities. Bremsstrahlung photons were generated and tracked. MCNP6 employed. 43

44 Methodology Monte Carlo Simulation PIMAL available (registration required) on U.S. Nuclear Regulatory Commission Radiation Protection and Computer Code Maintenance Program (RAMP) NRC RAMP Website RAMP Website ORNL inquiry: 44

45 Case 1: Public Transportation 1. Bus: Standing Faceto-Face Chest-to-Chest (10cm Separation) 2. Bus: Patient Seated in Front. (Whole Body Source) 3. Bus: Patient Seated Behind (Bladder Source) 4. Bus: Patient Seated Sideby-Side (Whole Body Source) 5. Bus: Patient Standing, Public Seated (Bladder Source) 6. Bus: Patient Seated, Public Standing (Bladder Source) 45

46 Case 2 - Nursing Home Nursing Home: Caregiver was seated 30 cm from the edge of the 131 I patient s bed (~125 cm from the patient s chest to the caregiver s chest). Nursing Home: 131 I patient and another nursing home resident were seated in adjacent beds 250 cm apart. Patient reclining in bed Caregiver 30cm from bed Profile view Aerial view Patient reclining in bed Roommate reclining in bed 46

47 Case 3: Hotel Room Hotel: 131 I patient and another hotel guest in an adjacent room were investigated for back-toback seated in bed position. Hotel: 131 I patient and another hotel guest in an adjacent room were investigated for back-toback lying flat positions in beds on opposite sides of the common wall. 47

48 Biokinetic Modeling 48 Revised 131 I model (Leggett, Radiation Research 174, 2010)

49 Biokinetic Model Single Void 1.20E E+00 Normal Thyroid (27%) DTC (5%) Hyperthyroid (80%) Retention per Bq Uptake 8.00E E E E E Time (Hours) Model predictions of retained fraction of 131 I in the body assuming single void at 4 hours after administration. 49

50 Biokinetic Model Continuous Void 1.20E E+00 Normal Thyroid (27%) DTC (5%) Hyperthyroid (80%) Retention per Bq Uptake 8.00E E E E E Time (Hours) Model predictions of retained fraction of 131 I in the body as a function of time assuming a continuous voiding pattern. 50

51 Biokinetic Model Periodic Void 1.20E E+00 Normal Thyroid (27%) DTC (5%) Hyperthyroid (80%) Retention per Bq Uptake 8.00E E E E E Time (Hours) Model predictions of retained fraction of 131 I in the body as a function of time assuming a 4-hour periodic voiding pattern.

52 Results: Effective Dose Rate on Public Transportation 7.00E E-05 Hyperthyroid Effective Dose Rate (msv/mbq-hr) 5.00E E E E E E+00 DTC No void-normal Thyroid No void-5% Uptake (DTC) No void-80% Uptake (Hyperthyroid) Void at 2 hours-normal Thyroid Void at 2 hours-5% Uptake (DTC) Void at 2 hours-80% Uptake (Hyperthyroid) Void at 4 hours-normal Thyroid Void at 4 hours-5% Uptake (DTC) Void at 4 hours-80% Uptake (Hyperthyroid) Void at 8 hours-normal Thyroid Void at 8 hours-5% Uptake (DTC) Void at 8 hours-80% Uptake (Hyperthyroid) Time Post-Administration (hrs.) Effective Dose Rate (msv/mbq-hr) on Public Transportation: Facing 10cm Separation. 52

53 Case 1: Public Transportation Results 131 I (DTC) Cancer Patient: Patient administered 7 GBq 131 I Assume patient voids once only Boards public transit immediately after voiding Rides with 100% occupancy factor Time Post- 131 I Administration Time to Exceed Dose (10 cm Facing) Time to Exceed Dose (Patient Seated Behind) 1 msv 5 msv 1 msv 5 msv No void <1 hr < 4 hrs < 4 hrs 18 hrs 2 hours 1 hr 5 hrs 4 hrs <24 hrs 4 hours >1 hr < 6 hrs 4 hrs >24 hrs (4.4 msv) 8 hours <2 hrs < 8 hrs 6 hrs >24 hrs (3.1 msv) 53

54 Case 1: Public Transit Results 131 I Hyperthyroid Patient: Patient administered 1.1 GBq 131 I Assume patient voids once only Boards public transit immediately after voiding Rides with 100% occupancy factor Time Post- 131 I Administration Time to Exceed Dose (10 cm Facing) Time to Exceed Dose (Patient Seated Behind) 1 msv 5 msv 1 msv 5 msv No void >4hrs <24 hrs <12 hrs (1.4 msv) >>24 hrs 2 hours <6hrs 24 hrs <12 hrs (1.2 msv) >>24 hrs 4 hours <6hrs 24 hrs <12 hrs (1.1 msv) >>24 hrs 8 hours <6hrs >24 hrs <12 hrs (1.1 msv) >>24 hrs 54

55 Case 2: Nursing Home Results 131 I Patient in Nursing Home in Bed: Continuous (first-order) voiding Conservative Case: 100% occupancy factor Exposure Scenario 2 hr. 90 d Caregiver (30cm from bed) Nursing Home Roommate (250 cm) DTC (msv) MBq Exposure Scenario 2 hr. 90 d Caregiver (30cm from bed) Nursing Home Roommate (250 cm) Hyperthyroid (msv) MBq 55

56 Case 3: Hotel Room Results 131 I Cancer Patient: Patient administered 7 GBq 131 I Patient assumed to check-in 12 hours after administration Periodic Voiding (every 4/8/12 hours) Conservative Case: 100% occupancy factor Time of Exposure Post- Administration Time to Exceed Dose (Seated) Time to Exceed Dose (Lying) 1 msv Max (240 hrs) 1 msv Max (240 hrs) 4 hours 144 hrs 1.2 msv N/A 0.4 msv 8 hours 216 hrs 1.0 msv N/A 0.4 msv 24 hours N/A 0.6 msv N/A 0.3 msv 56

57 Case 3: Hotel Room Results 131 I Hyperthyroid Patient: Patient administered 1.1 GBq 131 I Patient assumed to check-in 12 hours after administration Periodic Voiding (every 4/8/12 hours) Conservative Case: 100% occupancy factor Time of Exposure Post- Administration Time to Exceed Dose (Seated) 1 msv Max (240 hrs) Time to Exceed Dose (Lying) 1 msv Max (240 hrs) 4 hours <168 hrs 1.3 msv N/A 0.8 msv 8 hours 168 hrs <1.3 msv N/A 0.7 msv 24 hours < 192 hrs 1.1 msv N/A 0.7 msv 57

58 58 Hotel Housekeeper Internal Dose

59 Current Inhalation Dose to An Individual From Exposure to a Released Patient Regulatory Guide 8.39 provides the following estimate to the maximum internal effective dose to an individual from a released patient Based 10-6 Rule of thumb from Brodsky, HP 39, (1980) for workplace environments Multiplied by 10 to account for the most highly exposed individual and to add a degree of conservatism Supported by existing references at the time 59 5 D = 10 Q DCF i adm

60 Internal Intakes from Released Patients Household data Follows no obvious pattern from the limited data found in the literature. Contamination left by I-131 patients does not strictly scale with administered dose Personal habits are of great impact North, HP 104, (2013) Households of Thyroid Cancer Patients 43 people, 7 dogs Only 3 people had positive thyroid burdens Approximate transmission ranged from 6(10-6 ) to 2(10-5 ) 60

61 Contamination of Commode Hershey Medical Center 61

62 Hotel Housekeeper Internal Dose Estimate Scenario Typical time to clean a room is about 30 minutes Light activity breathing rate, 1.5 m 3 /hr Pathways considered Inhaling air concentration due to exhalation, etc. release from the patient and bedsheets in the room Patient leaves the room so the housekeeper can clean Patient Remains in the Room Puff release from removing bedding Dermal absorption due to contact with the toilet seat (forearm) 62

63 Hotel Room Parameters/Assumptions 300 ft 2 room floor space (typical ft 2 ) 8 ft ceilings, room volume = 68 m 3 Minimum Air changes = 4 hr -1 The Engineering Toolbox Could be much higher Toilet Seat treated by concentric ellipses Major ellipses IR inches, OR = 16 inches Minor ellipses IR = 8.25 inches, OR = inches 63

64 Air contamination rate Routes to air Nishizawa et al. HP 38, (1980) Exhalation Perspiration/Evaporation from contaminated patients and their material 1.8% evaporation rate Maximum air contamination rate varied from 1.4(10-5 ) to 1.2(10-7 ) per hr of the administered dose Need an effective half life Low end 0.57 days High end 3.86 days Grundel et al. RPD 129, (2008) 64

65 Airborne Inhalation in Room Exhalation from patient Based on data available in the literature The exhalation rate is estimated to be about 1.4(10-5 ) per hour of the activity remaining in the patient s body (max rate from Nishizawa et al.) The exhalation rate was used to calculate the airborne concentration in the room Resuspension from change of bedding (two sheets and coverlet) Based on data available in the literature about 8.3(10-4 ) of the activity in the patient ends up in the bedding Assume that 10-5 of the bedding contamination becomes airborne as a puff which is inhaled by the housekeeper 65

66 Bathroom Effective Dose to Housekeeper Scenario: Dermal Intake Assumptions Contamination is 100% removable Harrison in HP 9, (1963) Absorption of aqueous I-131 was 0.008% per cm 2 of contact per hour Toilet contact area with forearm = 77 cm 2 Housekeeper washes any remaining activity off 4 hours after contact is made 66

67 Dose to Hotel Housekeeper (Maximum Toilet Contamination Level) Pathway Breathing Contaminated Air Cancer patient Hyperthyroidism Dose (mrem) Bedding Puff Release Cancer patient Hyperthyroidism Skin Absorption Either 0.03 Total High Estimate Cancer patient Hyperthyroidism Cancer Patient Administration 7 GBq Hyperthyroidism Administration 1.1 GBq 67

68 68 CRPK Future Goals

69 69 The Crisis in Radiation Protection Radiation protection research groups have largely been disbanded or dramatically reduced in size. Low level of funding in this area for academic programs as well as labs. Consortium for the Advancement of Radiation Protection (CARP) CRPK MOU says little about the structure of the CRPK and how it will function. The CRPK could be used as a focal point for rebuilding the radiation protection education, training, and research efforts in the United States by forming a consortium of universities and national laboratories. Launching platform to provide the critical human resource and knowledge needs in radiation protection.

70 CARP Bring together the radiation protection research community remaining within the laboratory complex to engage in research and development as well as to participate in the training of the next generation of radiation protection professionals at all levels. Such a consortium could bring together the strengths of different university and laboratory programs in a strategic manner to accomplish a multifaceted research, educational and training agenda. 70

71 Radiation Protection Needs Workshop June 5-6, 2017 at ORAU, cosponsored by ORNL and HPS Track 1-1: Radiation protection issues with new fuel cycles and advanced technologies Track 1-2: Dosimetry Track 2-1: Radiation protection issues in medical physics Track 2-2: Instrumentation and operations Track 3-1: Radiation protection needs in national defense Track 3-2: Decontamination and decommissioning Track 4-1: Radiation in space Track 4-2: Environmental modeling Track 4-3: Radiation protection needs in emergency response Group Session - Low dose health effects 71

72 72 Questions?

73 Extra 73

74 Patient Release Criteria Criterion: Release patients administered licensed material if TEDE to a member of the public is not likely to exceed 500 mrem (5 msv). Guidance on calculation of dose to a member of public in contained in Regulatory Guide 8.39 Release of Patients Administered Radioactive Materials. The method in the guidance is a screening method which uses simplifying assumptions that tend to overestimate the risk. 74

75 Currently Used (point source from NCRP 37) ( tt / e P ) 34.6ΓQT o P 1 Dt () = 2 r Dt ( ) = accumulated exposure at time t, in R 34.6 = Conversion factor of 24 hrs/day times Γ = Q T r t o P = = the total integration of decay (1.44) Specific Gamma ray constant for a point source (R/mCi=hr at 1 cm) Initial activity of the point source in mci, at the time of the release Physical Half-life in days = distance from the point source to the point of interest in = exposure time in days cm 75

76 Reg Guide does the following Highest dose is obviously the dose to total decay 1 R = 10 msv or 1 rem ( tt / e P ) 1 1 Exposure rates constants and physical half lives are given in Appendix A of Reg Guide 8.39 Default activities at which patients are released are computed only using the physical half life But biological elimination can be considered (see Appendix B) For half lives greater than 1 day, person assumed to received 25% of the dose from total decay Shorter half lives, 75% - 100% of dose due to total decay 76

77 Release of Patients Based on Administered Activity (GBq) There is a table (internal dose is negligible) based on administered activity Can also released based on the retained activity using the physical half life Nursing infant is not considered in this table Based on Measured Dose calculation Dose rate at 1 m from the patient surface is not greater than values in the table. (record requires) Can use patient specific dose calculation 77

78 78

79 In Appendix B, more sophisticated approaches are found, but still a point source Effective half-life Three component but still a point source First 8 hours after administration Extrathyroidal component 8 hours to total decay Thyroidal component 8 hours to total decay 79

80 D F F E ( ) ( ) ( ( ) T ) P ( ) / / TP 34.6 ET 1 P e e E2FT ΓQ 1 1eff o = ( ) ( 0.33 )/ T 100cm P + e E2FT 2 2eff = Extrathyroidal uptake fraction = Thyroidal uptake fraction = Occupancy factor for the first 8 hours 80

81 Contaminated Surfaces and Skin Absorption Skin contamination comes exclusively from contact with the toilet seat. Removable toilet rim maximum contamination level of 911 Bq/cm 2 and a mean value of 193 Bq/cm 2 were derived from a study of in 50 patients in a Hershey Medical Center study (2001). There is no obvious correlation of surface contamination levels with administered dose. There are large variations in the contamination levels for the patients. Personal habits apparently influence contamination levels much more than administered dose. Using the maximum value, 23 Bq would be absorbed through the skin on of the housekeeper. 81

82 Improving Anatomy (?) 82

83 Thank You For Your Attention 83