심플한 템플릿1 _ Red Ver.

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1 방사선량및위험도평가 Radiation Doses and Hazard Assessment 양산부산대학교병원방사선종양학과전호상

2 Plan 5/06 Detection and Measurement of Radiation 1 5/13 Detection and Measurement of Radiation 2 5/20 Radiation Doses and Hazard Assessment 5/27 Industrial Application of Radiation 6/03 Medical Application of Radiation 6/10 Final Exam

3 9 Radiation Doses and Hazard Assessment

4 9 Radiation Doses and hazard assessment Radiation hazard (expression by consequences) Hereditary effect Illness in succeeding generation Somatic effect nature of exposure : acute or chronic time scale : short-term or long-term Radiation hazard (expression by exposure & duration) Deterministic effect Acute, life-threatening exposure A definite course of medical treatment Illness is certain Stochastic effect Minor acute or chronic Low-level exposure Probability of illness depend on dose

5 9.2 Dosimetric Quantities Radiation effect on matter : biological, chemical, even mechanical What s the best measure for radiation effect? fluence, energy fluence it s not enough to use

6 9.2 Dosimetric Quantities Dose To quantify biological radiation damage by measurement Named by medical radiologists It s not a precise term, but in a generic sense

7 9.2.1 Energy Imparted to the Medium Imparted energy of radiation to the medium Ionization and excitation and associated chemical changes Almost into thermal energy Radiation (E1) Medium (E1-E2) Radiation (E2)

8 9.2.2 Absorbed Dose Absorbed dose ( 흡수선량, D) Mean imparted energy E to the medium of mass m Standard unit : gray (Gy), 1 Gy = 1 J/kg Traditional unit : rad, 1 rad = 0.01 Gy Radiation (E1) Medium (E1-E2) Radiation (E2)

9 9.2.3 Kerma Kerma : Kinetic energy of radiation absorbed per unit mass In many situation, absorbed dose is difficult to calculate from radiation fluence Use only in connection with indirectly ionizing (uncharged) radiation E tr : sum of initial kinetic energy of all charged ionizing particles released by interaction of indirectly ionizing particles in mass m ( 비전리방사선으로인해발생된하전입자들의운동에너지의합 )

10 9.2.3 Kerma Absorbed dose vs Kerma A : Interaction ionization charged particle absorption B : Interaction partially absorption (B1) + Compton scatter (B2) Absorbed dose = A + B, Kerma = A + B1 A B Kerma 는전달된방사선에너지로인해 1 차적으로발생한하전입자운동에너지의양에관한것이지만, 흡수선량은그중에서최종적으로 흡수 된양에관한것이다. Kerma Absorbed dose

11 9.2.3 Kerma Absorbed dose = Kerma in charged particle equilibrium (CPE) Charged Particle Equilibrium (CPE) Radiation CPE A B A B A B no CPE

12 9.2.4 Calculating Kerma and Absorbed Doses Remember reaction rate density

13 9.2.4 Calculating Kerma and Absorbed Doses Fluence : Ф f(e) : 방사선에너지중 secondary charged particle 로전달된비율

14 9.2.4 Calculating Kerma and Absorbed Doses Photon Kerma and absorbed dose μ tr = μf

15 9.2.4 Calculating Kerma and Absorbed Doses Photon Kerma and absorbed dose Secondary charged particle Bremsstrahlung X-ray out of ROI μ tr μ en : correction for bremsstrahlung (see 7.3.4) Bremsstahlung is not contained by absorbed dose, but contained by Kerma

16 9.2.4 Calculating Kerma and Absorbed Doses

17 9.2.4 Calculating Kerma and Absorbed Doses Photon Kerma and absorbed dose Secondary charged particle Bremsstrahlung X-ray out of ROI μ tr μ en : correction for bremsstrahlung (see 7.3.4) Bremsstahlung is not contained by absorbed dose, but contained by Kerma

18 9.2.5 Exposure Exposure( 피폭량, X) It is applied only to photons (x-ray, gamma-ray) Definition : absolute value of ion charge produced by incident photons per unit air mass Unit : 1 R (roentgen) = 2.58x10-4 C / kg Kerma in air and exposure are very closely related The conversion factor, W, is almost energy independent For air, W = 33.85±0.15 ev / ion pair

19 9.2.5 Exposure μ en for the correction of bremsstrahlung (out of ROI!)

20 9.2.6 Relative Biological Effectiveness Relative Biological Effectiveness (RBE, 생물학적효과비 ) 같은 dose 라해도방사선의종류에따라생물학적효과가다름! Ex) alpha-ray 1Gy 는 X-ray 1Gy 보다인체에훨씬큰피해를줌 RBE = 특정생물학적영향을주는데필요한기준방사선의선량 같은생물학적영향을주는데필요한대상방사선의선량 기준방사선 (reference type of radiation) 250kVp x-ray or 1.25MeV 60 Co gamma-ray RBE 의예시 X-ray or gamma-ray : 1 Alpha-ray : 20 Proton (>2MeV) : 5

21 9.2.7 Dose Equivalent RBE 에영향을주는요소들이너무많음 사용이편리하지못함 QF (Quality Factor, 선질계수 ) 개념등장 RBE 와달리 QF 는특정생물학적효과와바로연결되는개념! 특히저선량방사선영향인암이나유전병에보편적으로적용가능 Dose Equivalent ( 등가선량, H) Standard SI unit : sievert (Sv) Traditional unit : rem (1 rem = 0.01 Sv)

22 9.2.8 Quality Factor 근본적으로 QF 의설정은주관적인요소가개입될수밖에없으나, 복잡하고정교한진단으로초기보다는많이객관화되었음 QF is defined for use in conventional and routine radiation protection! 현재 QF 의개념은 stopping power 나 LET (linear energy transfer) 의관점으로많이해석하지만, 대표적인 QF 들은아래와같음

23 9.2.8 Quality Factor

24 9.2.9 Effective Dose Equivalent Effective dose equivalent ( 유효등가선량, H E ) : ICRP (1977) In a human, different organs, different radiological effects!! To account for different organs and different dose equivalents Tissue weighting factor, T

25 9.2.9 Effective Dose Equivalent

26 Effective Dose Effective dose ( 유효선량, E) : ICRP (1991) 유효등가선량과거의같은개념이나, weighting factor 가다소차이

27 9.3 Natural Exposures for Humans 지구상에서는수많은자연방사선에노출됨 External source Cosmic radiation Radionuclides in the environment Internal source Radionuclides taken into the body by ingestion or inhalation Cosmic radiation ( 우주방사선 ) Interact with earth s atmosphere production of 3 H and 14 C radionuclides These cosmogenic radionuclides are produced at relatively uniform rates

28 9.3 Natural Exposures for Humans Naturally existing radionuclides (not of cosmic ray) 지구의나이 ( 수십억년 ) 와비견될정도의긴반감기 40 K 와 87 Rb 두가지의비중이절대적임 Decay chains of natural radionuclides Parent and daughter radionuclides as radiation sources Parent radionuclides 의반감기가지구의나이와비견될만함 인체영향주는 chain series : 238 U (44.6 억년 ), 232 Th (14.1 억년 ) Daughter products of Radon : 222 Rn and 220 Rn 전체자연방사선피폭중가장큰비중을차지함 폐암발병의주원인중하나로추정됨 (Radon gas)

29 9.3 Natural Exposures for Humans World average of human natural exposure : 2.4 msv Inhalation sources of high-let radiation : radon and its daughters

30 9.4 Health Effects from Large Acute Doses

31 9.4.1 Effects on Individual Cells A cell can be killed or prevented from division as the result of exposure which depends on many factors Dose rate and stopping power (or LET) Low dose rate : natural repair mechanism of cell More damage with high LET Cell s life cycle at the time of exposure More radiation sensitive in the process of division More cell death with rapidly reproducing cells

32 9.4.2 Deterministic Effects in Organs and Tissues Deterministic somatic effects D 50 : 50 th -percentile dose The risk or probability of suffering a effect as a function of radiation dose Depends on dose rate D th : a threshold dose (no effect below this dose)

33 9.4.3 Potential Lethal Exposure to Low-LET Radiation What is lethal dose? There is no simple answer Depend on too many factors Too sparse human data (extrapolation from animal data) LD x/y : y days 이내에피폭자의 x% 에게치명적인선량 Ex) LD 50/60 = 피폭후 60 일내에피폭자의 50% 에게치명적인선량 Defining of dose 1) free-field exposure in R unit for x or gamma-ray 2) Average absorbed dose to whole body 3) Mid-line absorbed dose (average near the abdomen)

34 9.4.3 Potential Lethal Exposure to Low-LET Radiation Representative effects of doses below the threshold of lethality

35 9.4.3 Potential Lethal Exposure to Low-LET Radiation The lethal effects of raidation exposure Extremely high doses (>500Gy) : instant death from enzyme inactivation or electrical response of heart 50~500 Gy : most symptons within minutes of exposure and death from neurological or cardiovascular failure ~50 Gy : Death from cardiac failure within a few days 6~50Gy : Death from damage to the gastrointestinal system

36 9.5 Hereditary Effects

37 9.5 Hereditary Effects Radiation-induced abnormalities was discovered by Hermann Muller (1927) : fruit flies study Very little information on radiation effect in humans In early 1950s, potential significance of hereditary illness was recognized by radiation protection standards (ICRP, NCRP) 1.7 msv limitation per year in excess of medical and background exposure Low-LET ionizing radiation at dose rate comparable to those of natural radiation environment

38 9.6 Cancer Risks from Radiation Exposures High doses of ionizing radiation is one of many causes of cancer in the human No excess cancer risk at doses less than about 0.2 Gy A large variation in the sensitivity of tissues and organs to cancer induction by radiation For whole-body exposure, solid tumors > leukemia Leukemia : 피폭후수년간은발병확률이증가하지만, 이후 30 년간은크게감소함 Solid cancer : 피폭후 10 년간종종발병하며, 그이후로도지속적발병

39 9.6 Cancer Risks from Radiation Exposures How cancer is induced is not understood fully It is clear 1) Ionizing radiation 만으로발병하는타입의 cancer 는없다 2) Cancer 발병은 initiation, promotion, progression 으로이어지는다단계과정이다 Initiation Cell nucleus 내에서일어나는 genetic coding disruption Cell reproduction 이어려울정도로심각해서는안됨 There is a latent period ( 잠복기 ) between exposure and onset of cancer 잠복기가 initiation promotion 과정을완전히설명하지는못하지만, 발암이다단계과정임을보여주는증거가됨 Progression Known to be enhanced by radiation Conversion of benign growth to malignant growth Attainment of malignant properties of established cancer

40 9.6.1 Estimating Radiogenic Cancer Risks Our knowledge of radiation induced cancer come from epidemiological studies ( 역학조사 ) Atomic bomb survivors : 91,000 survivors in Japan Radiation therapy patients Large occupational dose exposed Medical radiologists, industrial technicians, miners Women who ingested radium while painting dials in WW1

41 9.6.1 Estimating Radiogenic Cancer Risks Dose and dose rate effectiveness factor Cancer risk is concerned with low doses at low dose rates But the data is based on high doses at high dose rates How can we do assessment of cancer risk? A linear and no-threshold relationship between cancer risk and doses DDREF (a H /a L ) : the dose and dose rate correction factor

42 9.8 Radiation Protection Standards Need of radiation protection standards to protect workers and patients (20 세기초 ) The earliest standards were based on tolerable doses (no ill effects below this) Replacement with permissible doses (no appreciate body injury to any person during lifetime) by NCRP (National Council of Radiation Protection and Measurement) in USA

43 9.8.1 Risk-Related Dose Limits A ICRP report (1972) by Task Group on Dose Limits Low-level radiation exposure leads to stochastic hazards Radiation standard should be based on probabilistic assessments of radiation hazards Occupational radiation risk comparable with other occupational having risks of environmental risks ICRP (1977) Linear and no-threshold dose-response relationships for carcinogenic and genetic effects 1x10-4 probability per rem for malignant illness 4x10-5 probability per rem for hereditary illness For other radiation effects, absolute thresholds were assumed The concept of risk-based dose limits by 1977 ICRP and 1987 NCRP

44 9.8.1 Risk-Related Dose Limits For occupational risk An acceptable risk 50 per million workers per year A 40-year lifetime risk of 2 fatalities per 1000 workers (probability : 0.002) Annual dose is 10% of most high exposed individuals in radiation work The annual whole-body limit for stochastic effect : 5 rem/year average dose of 10% annually Lifetime risk Years Probability of illness per rem / = 5

45 9.8.1 Risk-Related Dose Limits For the public An acceptable risk 5 death per million persons per year A 70-year lifetime risk much below of 4 fatalities per 10,000 persons (probability < , let s assume ) The annual whole-body limit for stochastic effect : 0.5 rem/year Lifetime risk Years Probability of illness per rem / = 0.5

46 Homework

68 JOURNAL OF RADIATION PROTECTION, VOL.33 NO.2 JUNE 2008

JOURNAL OF RADIATION PROTECTION, VOL.33 NO.2 JUNE 2008 67 68 JOURNAL OF RADIATION PROTECTION, VOL.33 NO.2 JUNE 2008 Fig. 1. Atmospheric exposure pathway in the NukPacts model (Source : European Commission