C ORVALLIS A USTIN S EATTLE Ass ssessi essing ng Sk Skin in Dose se in th the Field eld from m Ra Radionuclide dionuclide Cont ntaminatio amination n on th the Bo Body Rolan and d Benk nke, PhD, , CHP Director of Business Development roland.benke@rcdsoftware.com 29 th Annual National Radiological Emergency Preparedness Conference Dose Assessment Series, April 4, 2019, Orlando, FL
C ORVALLIS A USTIN S EATTLE Radiological Contamination Screening • Important to incident response • Significant concern to o Public o Emergency workers o Medical care providers • Labor intensive • Common to many incidents 2
C ORVALLIS A USTIN S EATTLE Overarching Questions & Motivation • Handling high activity sources without shielding is dangerous, but what’s the potential for skin damage from intentional or uncontrolled radioactive material dispersal into the atmosphere? ? • What count rates from contamination are a medical concern for skin damage? • What new software features would provide the greatest benefits to responders in the field? 3
Potential to Fill Current Gap C ORVALLIS A USTIN S EATTLE Potential: Rapid assessment software for contaminated skin, clothing, & wounds • Contamination surveys yield o instrument count rate* o not dose rate • VARSKIN computer code o calculates skin dose o 30 years of U.S. NRC development • Dose rate much better for o triage o justifying medical treatment * Convertible to radionuclide activity per unit area if radionuclide identity & radionuclide-specific instrument calibration are known in the field 4
RCD ― Leader in Skin Dosimetry C ORVALLIS A USTIN S EATTLE • Experts in software development o C, C++, C#, FORTRAN o Python, Java, JavaScript, JSON o HTML, CSS, React, React Native, PHP o MATLAB, LabView, Unix shell, VHDL • VARSKIN computer code o developed by Dr. Hamby’s group over the last 10 years o maintained by Renaissance Code Development (RCD) Potential: Rapid assessment software for contaminated skin, clothing, & wounds • Potential fieldable smart phone app for skin dose 5
Technical Objective: Skin Dose Rate Conversion for Instrument Count Rate C ORVALLIS A USTIN S EATTLE • RCD demonstrates the solution by o developing survey meter efficiencies for large contaminated areas from point measurements of instrument count rate o calculating skin doses with VARSKIN • Necessary to quantify off-axis detection efficiency because larger contaminated areas imply greater off-axis contributions to instrument count rate 6
VARSKIN Background C ORVALLIS A USTIN S EATTLE • Developed for hot particles and contamination on or near skin • Shallow dose equivalent for highest contiguous 10 cm 2 or other areas • Electron (beta) and photon (gamma) dose modeling • Select source geometry as point, disk, cylinder, sphere, or slab • Air gap and multiple cover layers above skin allowed • Planar disk source selected to address varying areas of contamination in this assessment (i.e., skin curvature not modeled) 7
Method Summary & Example Measurement Data C ORVALLIS A USTIN S EATTLE • Calculated detection efficiency over center of uniformly contaminated area from radial point measurements 90 Sr/ 90 Y areal detection efficiency • 90 Sr/ 90 Y source o 24% for 1 cm 2 source o 18% for 10 cm 2 source o 4.4% for 100 cm 2 source o 0.45% for 1000 cm 2 source • Applied planar disk source geometry • Merged (1) VARSKIN skin doses per unit areal contamination and (2) contamination concentration necessary to induce a meter reading of 100,000 cpm • Compared skin dose rates for various scenarios 8
Important to Include Electrons C ORVALLIS A USTIN S EATTLE • Same radionuclide plotted, different encapsulation, very different efficiency • Source encapsulation significantly attenuates electrons (beta particles) • Vertical air gap of 1.3 cm • Investigation continued with thin foil sources for better representation of contamination on skin and clothing 5 9
Investigated Contamination Size C ORVALLIS A USTIN S EATTLE Small Point-like 10 cm 2 1 cm 2 Medium Large 100 cm 2 1000 cm 2 • Factor of 2 to 3 influence on skin dose rate from contamination size for same instrument count rate • Skin dose rate for highest contiguous 10 cm 2 exposed 10
Investigated Two Radionuclides C ORVALLIS A USTIN S EATTLE • Emission characteristics influenced skin dose rate by factor of 3 to 6 for same instrument count rate o Strontium-90/Yttrium-90 ( 90 Sr/ 90 Y), electron on (beta) a) emissions o Cesium-137/Barium-137m ( 137 Cs/ 137m Ba), phot otons ons (gamma mma) ) & electrons ons (beta) a) • Priority given to Radiological Dispersal Device (RDD) threats • Point-like, small, medium, and large contamination sizes considered RDD threat sources 11
Investigated Contamination on C ORVALLIS A USTIN S EATTLE Clothing versus Skin Deposition • Cotton clothing reduced skin dose rate by factor of 2 to 4 for same count rate • 0.4 mm cotton (0.036 g cm -2 ) • Point-like, small, medium, and large contamination sizes considered Above each point the instrument reads 100,000 cpm. Will skin dose be a concern … for both, for one, for neither? 12
C ORVALLIS A USTIN S EATTLE Conclusions of this Preliminary Assessment • Emergency guidance suggests 100,000 cpm* as a screening threshold for further medical evaluation (CRCPD Handbook) • Conversion factor for skin dose rate at the screening threshold o Less than 0.009 009 Gy Gy h -1 per r 100,0 0,000 00 cpm o Not more than 0.002 002 Gy Gy h -1 per r 100,0 0,000 00 cpm for most scenarios • Deterministic effects to unbroken skin expected at skin doses of 2 − 3 Gy • Sufficient time exists for self-decontamination or monitored decontamination at community reception centers to prevent skin damage • Irradiation damage to unbroken skin appears less critical for medical intervention at this screening threshold • Potential radionuclide uptake & internal doses justify further evaluation * Much lower levels are recommended for broken skin and contaminated wounds 13
VARSKIN Status & Prospects C ORVALLIS A USTIN S EATTLE • VARSKIN currently calculates skin dose rate from radionuclide activity and geometric inputs • We show how VARSKIN could be modified to produce skin dose rates from survey count rates in the field o Recall upper value 0.009 Gy h -1 to skin per 100,000 cpm* o Factor varied by more than an order of magnitude in this study o Single value could be useful for triage Feedback requested: Is there interest in field software to convert survey count ? rates from contamination on the body to skin dose rate or effective dose rate? * Screening threshold for electrons (beta) & photons (gamma); 14 lower levels apply to alpha particles
What features are most wanted? C ORVALLIS A USTIN S EATTLE Potential: Rapid assessment software for contaminated skin, clothing, & wounds • Current survey equipment does not provide dose rates from contamination on the body • Psychosomatic issues cannot be ignored, despite ruling out serious skin damage • Dose rates can be calculated, but is it better to emphasize GM pancake probes or other survey instruments during initial screening? • Contaminated wounds require much less radioactivity to become medically significant • REAC/TS implements contaminated wound modeling per NCRP Report 156 • What field software features do you want? 15
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