3/26/2017. Personal Dosimetry Monitoring and Dose Measurements. Agenda. Dosimetric Terms and Definitions Dose Limits External Dosimetry

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1 Speaker David Pellicciarini, CHP, MBA Vice President, Pharmacy Safety, Practice and Technical Operations Cardinal Health Nuclear Pharmacy Services Personal Dosimetry Monitoring and Dose Measurements David W. Pellicciarini, CHP, MBA Vice President, Pharmacy Safety, Practice and Tech. Ops. March 27, 2017 Disclosures Speaker is an employee of Cardinal Health Landauer, Inc. and Ludlum Measurements, Inc. are Cardinal Health vendors Several slides provided courtesy of Landauer, Inc., and obtained from the US NRC. Copyright 2016, Cardinal Health. All rights reserved. CARDINAL HEALTH, the Cardinal Health LOGO and ESSENTIAL TO CARE are trademarks or registered trademarks of Cardinal Health. 2 Agenda Dosimetric Terms and Definitions Dose Limits External Dosimetry Personal Dosimeters Self-reading Dosimeters Internal Dosimetry (in Nuclear Pharmacy) Dosimetric Terms and Definitions 4 3 International Standards International Standards International Commission on Radiation Units and Measurements (ICRU) The group formally charged with defining the quantities and units employed in radiation protection International Commission on Radiological Protection (ICRP) Make recommendations regarding radiation protection, usually employing ICRU terminology, but sometimes get involved in defining radiological quantities and units. Key Publications Recommendations of the International Commission on Radiological Protection. ICRP Publication 26 (1977) Recommendations of the International Commission on Radiological Protection. ICRP Publication 60 (1990) Recommendations of the International Commission on Radiological Protection. ICRP Publication 103 (2008) 5 6 1

2 U.S. Regulatory Agencies Dosimetric Quantities Almost all U.S. regulatory agencies employ the quantities and units of ICRP 26. The exception is the Department of Energy, which employs the terminology of ICRP 60. Exposure (X) Units: roentgen (R), coulombs/kilogram (C/kg) Absorbed Dose (D) Units: rad, gray(gy), joules/kilogram (J/kg) Dose Equivalent, aka Equivalent Dose (H or DE) Units: rem, sievert (Sv) 7 8 Exposure (X) Exposure Units: roentgen (R), coulombs/kilogram Unit conversions: 1 R = 2.58 x 10-4 C/kg The quantity exposure reflects the intensity of gamma ray or x-rays and the duration of the exposure. More specifically, it is a measure of the charge on the ions of one sign (negative or positive) resulting from the interaction of gamma ray and x-ray photons in a specified mass of air Exposure (X) and Exposure Rate ( ) Absorbed Dose (D) The quantity is only defined for photons (e.g., gamma rays and x-rays). The quantity is only defined in air. The exposure of other materials (e.g., tissue) should not be expressed in units of exposure rate (e.g., mr/hr). Units: rad gray (Gy) joules/kilogram Unit conversions: 1 Gy = 1 J/kg = 100 rads

3 Absorbed Dose (D) Absorbed Dose (D) The quantity absorbed Dose (D) is a measure of the amount of radiation energy absorbed per unit mass (e.g., joules/kilogram or ergs/gram). It applies to all types of radiation, e.g., x-rays, gamma rays, betas, alphas, neutrons The absorbed dose reflects the energy deposited per unit mass, not the total energy: A 100 kg person absorbing 100 joules of energy has an absorbed dose of 1 (100 rads) A 50 kg person absorbing the same energy has an absorbed dose of 2 Gy (200 rads). The absorbed dose can be calculated for any material, e.g., air, water, tissue, lead The absorbed dose is material specific The absorbed dose to human tissue from gamma rays or x- rays will be greater than the absorbed dose to air in the same situation Absorbed Dose and Exposure Dose Equivalent (H) An exposure of 1 roentgen equates to an absorbed dose 0.88 rads in air. Units: rem sievert (Sv) An exposure of 1 roentgen equates to an absorbed dose of approximately 1 rad in tissue. Unit conversions: 1 Sv = 100 rems Dose Equivalent (H) Dose Equivalent (H) The quantity dose equivalent is an administrative concept employed for the purpose of radiation protection. It attempts to be a measure of the long term biological consequences for humans of a given exposure to radiation. This is why the regulatory limits are expressed as a dose equivalent rather than exposure or absorbed dose. The dose equivalent is calculated as follows: H = D Q H is the dose equivalent (e.g., rems, sieverts) D is the absorbed dose to human tissue (e.g., rads, gray) Q is the quality factor Internationally, the quality factor (Q) has been replaced by the radiation weighting factor w R : H = D w R It is defined for routine radiation protection applications. It should not be used in the numerical assessment of high level exposures (ICRU 51)

4 Quality Factor Dose Equivalent Permutations Type of radiation Quality factor (Q) X-, gamma, or beta radiation 1 Alpha particles, multiple-charged particles, fission fragments and heavy particles of unknown charge 20 Neutrons of unknown energy 10 High-energy protons 10 Deep dose equivalent (DDE or H d ) Lens dose equivalent (LDE) Shallow dose equivalent (SDE or H s ) Committed dose equivalent (CDE or H T,50 ) Committed effective dose equivalent (CEDE or H E,50 ) Total organ dose equivalent (TODE) Total effective dose equivalent (TEDE) 10 CFR DDE and SDE CDE and TODE DDE: applies to external whole-body exposure, is the dose equivalent at a tissue depth of 1 cm (1000 mg/cm 2 ). CDE (H T,50 ) means the dose equivalent to organs or tissues of reference (T) that will be received from an intake of radioactive material by an individual during the 50-year period following the intake. LDE: applies to the external exposure of the lens of the eye and is taken as the dose equivalent at a tissue depth of 0.3 centimeter (300 mg/cm 2 ). Total Organ Dose Equivalent SDE: applies to the external exposure of the skin of the whole body or the skin of an extremity, is taken as the dose equivalent at a tissue depth of centimeter (7 mg/cm 2 ). TODE = DDE + CDE CEDE and TEDE CEDE (H E,50 ) is the sum of the products of the weighting factors applicable to each of the body organs or tissues that are irradiated and the committed dose equivalent to these organs or tissues (H E,50 = ΣW T H T.50 ). Dose Limits Total Effective Dose Equivalent TEDE = DDE + CDE

5 Dose Limits for Adults Dose Type Limit Notes TEDE TODE LDE 5 rems 50 rems 15 rems Whichever is more restrictive External Dosimetry: Personal Dosimeters SDE, WB or ME 50 rems Remember: TEDE = Outside + Inside {for the whole body} TODE = Outside + Inside {for an organ} Types of Dosimeters Dose of Record Processed Optically stimulated luminescence (OSL) Film (well on the decline) Self-reading Electronic dosimeters Pocket (ion chamber) dosimeters 10 CFR (d) All personnel dosimeters (except pocket ionization chambers and those dosimeters used to measure the dose to the extremities) that require processing to determine the radiation dose and that are used by licensees to comply with [the regulations and license conditions] must be processed and evaluated by a dosimetry processor-- (1) Holding current personnel dosimetry accreditation from the National Voluntary Laboratory Accreditation Program (NVLAP) of the National Institute of Standards and Technology; When scintillators (e.g., NaI, ZnS) absorb energy imparted by ionizing radiation, they immediately release some of this energy as light. For each particle of radiation interacting with the scintillator, a flash of light (scintillation) is produced. The greater the energy absorbed by the material, the brighter the flash. When thermoluminescent materials (e.g., LiF) absorb energy, much of this energy is trapped rather than released immediately. The material must be heated for this trapped energy to be released as light. The total amount of light emitted during the heating process reflects the absorbed dose (i.e., the radiation energy absorbed). The emitted light can t be used to determine the energy deposited by individual particles of radiation. It reflects the total energy deposited by all the radiation interactions in the TL material

6 TL materials suitable for dosimetry: LiF Li 2 B 4 O 7 CaF 2 CaSO 4 Al 2 O 3 When impurities are added intentionally to a TL material, the latter is said to be "doped." The added impurities are referred to as activators. The identity of the activator might appear in parentheses after the formula for the TL material, e.g., LiF(Mg), or following a colon, e.g., LiF:Mg. Electrons located at these impurities may possess energies that electrons in other parts of the solid cannot, i.e., they may possess energies in the band gap Two types of impurities: electron traps hole traps Electron traps are impurities with insufficient electrons to complete covalent bonds with the surrounding atoms. Until filled by an electron, there is a hole at the electron trap. In the following figures, the hole is symbolized with a + sign. The idea is that the material has a specific number of different types of impurities. Electrons at these impurities possess energies at different levels (depths) in the band gap. Electron traps Hole Traps are impurities with more unpaired electrons than needed to form covalent bonds with the surrounding atoms. Hole traps The extra electrons at such impurities are more loosely bound than those forming covalent bonds. Their energies are also higher, just above those in the valence band

7 Irradiating a TLD Irradiating a TLD Irradiated TLD Heating an irradiated TLD: one pathway Heating an irradiated TLD: second pathway Heating an irradiated TLD: second pathway

8 Heating an irradiated TLD: second pathway Glow curves The temperature at which a peak is produced reflects the depth of the corresponding trap. A peaks height reflects the number of electrons in that trap Energy response Optically Stimulated Luminescence Innovation in Technology Slides provided courtesy of Landauer, Inc. 45 History of OSL OSL pioneered in 1992 Pacific Northwest National Laboratory (PNNL) Oklahoma State University (OSU) LDR Technology licensed to LANDAUER Al 2 O 3 :C crystals grown by LANDAUER First OSL dosimeters distributed in 1996 OSU OSL Al 2 O 3 :C PNNL

9 OSL Technology Timeline LANDAUER Aluminum Oxide Manufacturing Luxel InLight 2004 InLight OSLN 2009 RadWatch 2011 Luxel Personnel Monitoring Al 2 O 3 :C Detectors How Stimulation and Analysis Works Polyester Substrate Al 2 O 3 :C powder Polyester Cover Tape 0.3 mm thick The amount of radiation exposure is measured by stimulating the Al 2 O 3 material with green light from either a laser or light emitting diode source. The resulting blue light emitted after stimulation indicates the level of radiation exposure. This can be done repeatedly to verify a radiation exposure or to accumulate a total dose over time Conceptual Energy Diagram After Irradiation Thermoluminescence Dosimetry (TLD) Dosimetric Traps Dosimetric Traps Luminescence Centers Luminescence Centers

10 Optically Stimulated Luminescence (OSL) Features of OSL Dosimetric Traps Non-destructive analysis enables Verification read Mid wear period read Emergency read Incremental and cumulative dose Luminescence Centers 55 Radiation Response OSL responds to beta and photons (X and gamma rays) OSLN responds to beta, photons, and neutrons 1 n 0 56 Luxel+ Dosimeter Imaging Diagnostic Tool Al 2 O 3 Detector Material Dosimeter not being worn Dosimeter being worn Copper filter Aluminum filter Plastic filter Open window Imaging filter Filter Pack 57 Static Dynamic 58 Pocket and Electronic Dosimeters Examples of Response Matrix Self reading pocket dosimeter Low energy beta particles (i.e., 204 Tl) Penetrates open window only and is blocked by the other filters. High energy beta particles (i.e., 90 Sr) Penetrates open window, plastic, and aluminum filters. The open window relative response to shallow dose is 1.12 while the plastic and aluminum relative response is approximately The beta does not possess enough energy to penetrate the copper filter position. High-energy photons (e.g., 137 Cs kev) Penetrates all filters equally. Photons around 40keV (80 kvp) Open window and plastic readings similar Aluminum reading less than the plastic Copper reading having much lower response compared to the other 3 readings

11 Pocket and Electronic Dosimeters Pocket and Electronic Dosimeters Self reading pocket dosimeter Self reading pocket dosimeter (ion chamber type) Pros Operator can directly and immediately read the dose Fairly flat energy response Simple - no buttons, batteries, moving parts Source: ORAU Cons Susceptible to discharge via mechanical shock No audible alarm Low degree of precision eyeballing on a course analog scale Pocket and Electronic Dosimeters Pocket and Electronic Dosimeters Electronic dosimeter Electronic dosimeter Pros Operator can directly and immediately read the dose Audible alarms and chirps Cons Batteries required Some susceptible to radio interference Operator can impact success of use Bioassay Remember that the whole body dose limits are based on outside + inside Internal Dosimetry: Thyroid Bioassay OSL, TLDs give the outside For the inside Nuclear pharmacies handling radioactive materials that may result in the operator receiving an intake of those radioactive materials may be required to perform bioassay, i.e., measure the amount of radioactive material taken in to the worker s body

12 Bioassay Thyroid Bioassay In nuclear pharmacy, the isotopes of interest are typically I-131 I-123 Iodine trapped by the thyroid provides a convenient method to measure the overall intake of I-131 into a worker s body. Ludlum Model 2200 Scaler Flat scintillation probe Neck phantom Thyroid Bioassay Thyroid Bioassay A = Net count rate Counting system efficiency cpm cpm μci μci Intake (μci) x 5 rem CEDE = SALI(μCi) where SALI is the stochastic annual limit on intake Intake = A(t) IRF(t) where IRF(t) = intake retention fraction at time t Intake(μCi) x 50 rem CDE = NALI(μCi) where NALI is the non-stochastic annual limit on intake Bioassay References Thyroid Bioassay US NRC Regulatory Guide 8.9, Acceptable Concepts, Models, Equations, and Assumptions for a Bioassay Program US NRC RG 8.20, Table 1: US NRC Regulatory Guide 8.20, Applications of Bioassay for Radioiodine US NRC Regulatory Guide 8.34, Monitoring Criteria and Methods to Calculate Occupational Radiation Doses NUREG/CR-4884, Interpretation of Bioassay Measurements Intake retention fractions

13 Thyroid Bioassay Final thought US NRC RG 8.20, Table 2: NUREG 1556, Vol 13 Consolidated Guidance About Materials Licenses Program-Specific Guidance About Commercial Radiopharmacy Licenses The licensee should perform an evaluation of the dose the individual is likely to receive prior to allowing the individual to receive the dose (prospective evaluation). (emphasis added) Thank you