Dose Limits for Exposure to Ionizing Radiation PDF

Dose Limits for Exposure to Ionizing Radiation  Dx Wr Gamma QF 1 EgD 65-17 =...

Dose Limits for Exposure to Ionizing Radiation  Dx Wr Gamma QF 1 EgD 65-17 = = = 1 pg ↓. I Beta QF = ↓ = Equivalent Dose Alpha = QF = 20 for Dosage limits Factors Remember Dose Limits ↓ Weighting * EfD BXWrXW Dose = I ↓ factor Dose Effective ↓ weighted ↓ tissue Dose weighted  Exposure of the general public, patients, and radiation workers to ionizing radiation must be limited in order to minimize the risk of harmful biologic effects.  Occupational and nonoccupational effective dose (EfD) limits and equivalent dose (EqD) limits for tissues and organs such as the lens of the eye, skin, hands, and feet have been developed for radiation safety purposes. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 2  NRC = Is a secondary regulation Dose Limits (Cont.)  An EfD limiting system has been incorporated into Title 10 of the Code of Federal Regulations, Part 20, a document prepared and distributed by the U.S. Office of the Federal Register. The rules and regulations of the Nuclear Regulatory Commission (NRC) and fundamental radiation protection standards governing occupational radiation exposure are included in this document. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 3  Basis of EfD Limiting System  Basis of the EfD limiting system  Concept of radiation exposure and of the associated risk of radiation-induced malignancy  Resource for revised recommendations:  National Council on Radiation Protection and Measurements (NCRP) Report No. 116  International Commission on Radiological Protection (ICRP) Report No. 60  Future radiation protection standards are expected to continue to be based on risk. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 4  Basis of EfD Limiting System (Cont.)  Reasons medical imaging professionals must be familiar with previous, existing, and new guidelines for radiation safety  They share the responsibility for patient safety from radiation exposure.  They are subject to radiation exposure in the performance of their duties.  Radiographers may obtain the required knowledge by becoming familiar with the functions of the various advisory groups and regulatory agencies. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 5  Radiation Protection Standards Organizations  There are four major organizations responsible for evaluating the relationship between radiation EqD and induced biologic effects. These organizations are also concerned with formulating risk estimates of somatic and genetic effects of irradiation. facilites = Regulatorfine people Can facilites = Non regulator Only write reports Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 6 Objectives of the NCRP Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 7  U.S. Regulatory Agencies  After radiation protection standards have been determined, responsible agencies must enforce them for the protection of the general public, patients, and occupationally exposed personnel. paperwork filed here Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 8  Radiation Safety Program  Facilities providing imaging services must have an effective and detailed radiation safety program to ensure adequate safety of patients and radiation workers.  Implementation of an effective program  Begins with administration of the facility  Must provide resources necessary for creating and maintaining program Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 9  Radiation Safety Committee (RSC)  NRC mandates that an RSC be established for the facility  Functions of the RSC:  Provides guidance for the program  Facilitates ongoing operation of the program  Selects a qualified person to serve as a radiation safety officer (RSO) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 10  RSO  An RSO should  Oversee the program’s daily operation  Provide for formal review of the program each year  RSO is normally a  Medical physicist  Health physicist  Radiologist  Other individual qualified through adequate training and experience  RSO has been designated by a health care facility and approved by the NRC and the state. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 11  Responsibilities of the RSO  Specifically responsible for developing an appropriate radiation safety program for the facility that follows internationally accepted guidelines for radiation protection  Must ensure that the facility’s operational radiation practices are such that all people, especially those who are or could be pregnant, are adequately protected from unnecessary exposure Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 12  Responsibilities of the RSO (Cont.)  To fulfill their responsibility, management of the facility must grant the RSO the authority necessary to implement and enforce the policies of the radiation safety program.  RSO must also  Review and maintain radiation-monitoring records for all personnel  Be available to provide counseling for individuals Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 13 Required Training and Experience for an RSO  Necessary training and experience for an RSO are described in sections 10 CFR 35.50 and 10 CFR 35.900 of the Code of Federal Regulations.  There are three training pathways for an RSO. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 14  Authority of the RSO  10 CFR 35.24 requires that the licensee provide the RSO  Sufficient authority  Organizational freedom  Management prerogative to perform certain duties Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 15  Authority of the RSO (Cont.)  Licensee must establish, in writing, the authority, duties, and responsibilities of the RSO.  RSO is responsible for day-to-day supervision of the facility’s radiation safety program.  RSO must have independent authority to stop operations that are considered unsafe.  RSO must be given adequate time and resources and have a sufficient commitment from management to ensure that radioactive materials are used in a safe manner. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 16  Authority of the RSO (Cont.)  NRC requires the name of the RSO on the facility’s radioactive materials license to ensure that licensee management has always identified a responsible, qualified person who can directly interact with the NRC during inspections and also concerning any inquiries about the facility’s safety program.  Usually the RSO is a full-time employee of the licensed facility.  Training for an RSO is covered in 10 CFR 35  See Appendix H in textbook for a list of requirements. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 17 Radiation Control for Health and Safety Act of 1968  Act passed by U.S. Congress in 1968  Public Law 90-602  Purpose of law:  To protect the public from the hazards of unnecessary radiation exposure resulting from electronic products and diagnostic x-ray equipment  Act permitted the establishment of the Center for Devices and Radiological Health (CDRH) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 18 Radiation Control for Health and Safety Act of 1968 (Cont.)  CDRH falls under the jurisdiction of the Food and Drug Administration (FDA).  CDRH is responsible for conducting an ongoing electronic product radiation control program.  Law 90-602 does not regulate the diagnostic x-ray user. It is strictly an equipment performance standard. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 19 Code of Standards for Diagnostic X-Ray Equipment  Went into effect on August 1, 1974  Applies to complete systems and major components manufactured after that date Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 20  As Low as Reasonably Achievable (ALARA) Concept  Principle put forth in 1954 by the NCRP  Radiation exposure should be kept “as low as reasonably achievable” with consideration for economic and societal factors  Described by NCRP as “the continuation of good radiation protection programs and practices which traditionally have been effective in keeping the average and individual exposures for monitored workers well below the limit” Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 21  ALARA Concept (Cont.)  Also known as optimization  Medical imaging personnel and radiologists share the responsibility to keep occupational and nonoccupational dose limits ALARA.  EfDs and EqDs should be well below maximal allowable levels.  Goal can usually be achieved through the employment of proper safety procedures performed by qualified personnel. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 22  ALARA Concept (Cont.)  Procedures should be clearly described in a facility’s radiation safety program.  To define ALARA, health care facilities usually adopt investigational levels (Level I and Level II). Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 23  Model for the ALARA Concept  An extremely conservative model with respect to the F relationship between ionizing radiation and potential risk  Relationship is assumed to be completely linear and without any Figure 10-02. Dose-Response Curve. Hypothetical linear (straight-line) nonthreshold curve for radiation threshold dose-response relationship. The straight-line curve passing through the origin in this graph indicates both  In the interest of safety, that the response to radiation (in terms of biologic risk of injury should be effects) is directly proportional to the dose of radiation and that no known level of radiation dose exists below overestimated rather which absolutely no chance of sustaining biologic damage is evident. than underestimated Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 24  FDA White Paper Published In February 2010  FDA supports the premise that “each patient should get the right imaging exam, at the right time, with the right radiation dose.”  FDA announced “the launch of a cooperative Initiative to Reduce Unnecessary Exposure from Medical Imaging.”  Working in conjunction with their partners, the FDA intends to take specific action.  By coordinating these efforts, the FDA will be able to “optimize patient exposure to radiation from certain types of medical exams, and thereby reduce risks while maximizing the benefits of these studies.” Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 25  Consumer-Patient Radiation Health and Safety Act of 1981  Title IX of Public Law 97-35 (see Appendix I in textbook)  Provides federal legislation requiring the establishment of minimal standards for the accreditation of education programs for people who perform radiologic procedures and certification of such people  Purpose of federal act is to ensure that standard medical and dental radiologic procedures adhere to rigorous safety precautions and standards  Individual states are encouraged to enact similar statutes and administer certification and accreditation programs based on the standards therein  Because no legal penalty exists for noncompliance, many states, unfortunately, have not responded with appropriate legislation. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 26  Goal For Radiation Protection  NCRP Report No. 116 enunciates the goal of radiation protection, which reads as follows.  “To prevent the occurrence of serious radiation- induced conditions (acute and chronic deterministic effects) in exposed persons and to reduce stochastic effects in exposed persons to a degree that is acceptable in relation to the benefits to the individual and to society from activities that generate such exposures.” Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 27 Categories of Radiation-Induced Responses  Two all-inclusive categories encompass the radiation-induced responses of serious concern in radiation protection programs.  Deterministic effects You they : can tell will be affected of but still roll  Stochastic (probabilistic) effects : Not for dice sure , possible Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 28  Radiation-Induced Responses of Concern in Radiation Protection. it generations get Deterministic effects future   Biologic somatic effects of ionizing radiation that can be directly related to the dose received  Exhibit a threshold dose below which the response does not normally occur and above which the severity of the biologic damage increases as the dose increases  These effects typically occur only after large doses of radiation. However, they could also result from long-term individual low doses of radiation sustained over several years.  Effects can be either early deterministic effects or late deterministic effects Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 29  Radiation-Induced Responses Of Concern In Radiation Protection the effect get Stochastic (probabilistic) effects we   Mutational, nonthreshold, randomly occurring biologic somatic changes; mutational refers to changes to somatic cells that would affect the individual when the cells divide, as opposed to genetic, which refers to changes to germ cells that would affect future generations  Their chances of occurrence increase with each radiation exposure.  Examples Cancer Genetic alterations  May be demonstrated with the use of both the linear and the linear-quadratic dose-response curves Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 30 Summary of Both Early and Late Deterministic and Stochastic (Probabilistic) Effects Dividing factor is 6 months Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 31 Objectives of Radiation Protection * you can prevent deterministiceffectto  Radiation protection has two explicit threshold * objectives.  To prevent any clinically important radiation- induced deterministic effect from occurring by adhering to dose limits that are beneath the threshold levels  To limit the risk of stochastic responses to a conservative level as weighted against societal needs, values, benefits acquired, and economic considerations Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 32  Current Radiation Protection Philosophy  Both genetic and somatic responses to ionizing radiation were considered in developing the present EfD limiting ↓ recommendations. maximum allowed radiation  Current radiation protection philosophy is based on the assumption that a linear nonthreshold relationship exists between radiation dose and biologic response. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 33  Current Radiation Protection Philosophy (Cont.)  Even the most minuscule dose of radiation has a non-zero potential to cause some harm.  Ionizing radiation possesses a beneficial and a destructive potential.  When employed in the healing arts for the welfare of the patient, the potential benefit of exposing the patient to ionizing radiation must far outweigh any potential risk. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 34  Risk  Risk in the medical imaging industry  Risk in general terms  The probability of injury, ailment, or death resulting from an activity  Risk, in the medical imaging industry, after irradiation, is viewed as the possibility of inducing a radiogenic cancer or genetic defect. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 35  EfD Limiting System  Current method for assessing radiation exposure and associated risk of biologic damage to radiation workers and the general public  EfD limit concerns the upper boundary dose of ionizing radiation that results in a negligible risk of bodily injury or hereditary damage.  EfD limits may be expressed for whole-body exposure, partial-body exposure, and exposure of individual organs. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 36 EfD Limiting System (Cont.) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 37  EfD Limiting System (Cont.)  Separate limits are set for occupationally exposed individuals and for the general public.  The sum of both the external and internal whole-body exposure is considered when EfD limits are established.  Upper limits are designed to minimize the risk to humans in terms of deterministic and stochastic effects.  Upper limits do not include natural background and medical exposure. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 38  EfD Limiting System (Cont.)  Upper boundary radiation exposure limits for occupationally exposed persons are associated with risks that are similar to those encountered by employees in other industries such as manufacturing, trade, or government, which are generally considered to be reasonably safe.  Radiation risks are derived from the complete injury caused by radiation exposure. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 39  Revised Concepts of Radiation Exposure and Risk  Are responsible for more recent changes in NCRP recommendations for limits on exposure to ionizing radiation  Many conflicting views exist on assessing the risk of cancer induction from low-level radiation exposure.  The trend has been to create more rigorous radiation protection standards.  Adoption of the EfD limiting system is a direct consequence of this conservatism.  Benefit obtained from any diagnostic imaging procedure must always be weighed against the risk that is taken. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 40  have X-ray techs 10 days shortened Occupational Risk than the average person  Occupational risk associated with radiation exposure may be equated with occupational risk in other industries that are generally considered reasonably safe. That risk is generally estimated to be a 2.5% chance of fatal accident over an entire career. The lifetime fatal risk in hazardous occupations such as logging and deep sea fishing is many times greater. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 41  Occupational Risk (Cont.)  To ensure that the hazard to radiation workers is no greater than the hazard to the general working public, the NCRP proposes that radiation protection programs for radiation workers be designed to prevent individual workers from having a total external plus internal cumulative EfD in excess of their age in years times 10 millisievert (mSv). Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 42 Vulnerability of the Embryo-Fetus to Radiation Exposure  Embryo-fetus in utero is particularly sensitive to radiation exposure.  Epidemiologic studies of atomic bomb survivors exposed in utero provided conclusive evidence of a dose-dependent increase in the incidence of severe mental retardation for fetal doses greater than approximately 0.4 Sievert (Sv).  Greatest risk for radiation-induced mental retardation occurred when the embryo-fetus was exposed 8 to 15 weeks after conception. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 43 Basis for the EfD Limiting System  Concept underlying radiation protection  Any organ in the human body is vulnerable to damage from exposure to ionizing radiation.  Some organs are more sensitive to radiation than others.  Every organ is at some risk because of the assumed random nature of somatic or hereditary radiation- induced effects.  EfD limiting system includes, for the determination of EqD for tissues and organs, all radiation-vulnerable human organs that can contribute to potential risk, rather than only those human organs considered critical. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 44  Tissue Weighting Factor (WT)  EfD limiting system is an attempt to equate the various risks of cancer and hereditary effects to the tissues or organs that were exposed to radiation.  Because various tissues and organs do not have the same degree of sensitivity to these effects, the system employed must compensate for the differences in risk from one organ to another. Therefore, a tissue weighting factor (WT) is used.  WT “indicates the ratio of the risk of stochastic effects attributable to irradiation of a given organ or tissue (T) to the total risk when the whole body is uniformly irradiated.” Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 45  WT (Cont.) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 46 Current NCRP Recommendations  NCRP reports  Published reports reflect the current position and recommendations of the NCRP on radiation protection standards.  Annual occupational EfD limit  An annual occupational EfD limit of 50 mSv (not including medical and natural background exposure) has been established for the whole body, with an added recommendation that the lifetime EfD in mSv should not exceed 10 times the occupationally exposed person’s age in years. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 47  Current NCRP Recommendations (Cont.)  Cumulative EfD (CumEfD) limit  A radiation worker’s lifetime EfD must be limited to his or her age in years times 10 mSv.  EfD limits do not include radiation exposure from natural background radiation or medical procedures.  EfD limits include the possibility of both internal and external exposure.  Medical imaging personnel hardly ever receive EqDs that are close to the annual EfD limit. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 48  Current NCRP Recommendations (Cont.) Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 49  Current NCRP Recommendations (Cont.)  Collective EfD (ColEfD)  Has been designed for use in the description of population or group exposure from low doses of different sources of ionizing radiation  Is determined as the product of the average EfD for an individual belonging to the exposed population or group and the number of persons exposed  Person-seivert is the unit to express this quantity. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 50  Current NCRP Recommendations (Cont.)  ICRP for downward revision of the annual EfD limit  Levels of ionizing radiation formerly considered acceptable by the ICRP have been revised downward. In 1991 ICRP recommended the reduction of the annual EfD limit for occupationally exposed people from 50 mSv to 20 mSv as a result of newer information obtained regarding the Japanese atomic bomb survivors in whom the risk of radiation from the atomic bomb detonations was estimated to be approximately three to four times greater (more damaging) than previously estimated.  NCRP is still considering the possibility of reducing exposure standards. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 51  Current NCRP Recommendations (Cont.)  Limits for nonoccupationally exposed individuals  NCRP also sets limits for nonoccupationally exposed individuals who are not undergoing medical imaging procedures.  A limit also has been set for individual members of the general public not occupationally exposed.  NCRP-recommended annual EfD limit is 1 mSv for continuous or frequent exposures from artificial sources other than medical irradiation and natural background and a limit of 5 mSv annually for infrequent exposures. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 52  Current NCRP Recommendations (Cont.)  Limits for pregnant female radiation workers  To reduce exposure for pregnant workers and control the exposure to the unborn during potentially sensitive periods of gestation, the NCRP now recommends a monthly EqD limit not exceeding 0.5 mSv per month to the embryo-fetus and a limit during the entire pregnancy not to exceed 5.0 mSv after declaration of the pregnancy.  The monthly limit is more stringent.  Deterministic effects such as small head size and mental retardation are expected to be statistically negligible if the EqD remains at or below the recommended limit. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 53 Current NCRP Recommendations (Cont.)  Limits for education and training purposes  The limit for any education and training of individuals under the age of 18 years is an EfD of 1 mSv annually.  Limits for tissues and organs exposed selectively or together with other organs  Limits have been set to prevent excessive doses to tissues and organs exposed selectively or together with other organs.  150 mSv to the crystalline lens of the eye  500 mSv for localized areas of the skin, the hands, and the feet  Negligible Individual Dose  To provide a low-exposure cutoff level so that regulatory agencies may dismiss a level of individual risk as being of negligible risk, an annual negligible individual dose (NID) of 0.01 mSv/year per source or practice has been set. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 54  Action Limits  Personnel dosimeter readings should be well below a tenth of the maximum EfD limits, even for those technologists who receive the most exposure.  Health care facilities, such as hospitals, establish their own internal action limits. These limits are set at levels far below the actual limits. These limits are meant to trigger an investigation that should uncover the reason for any unusually high exposure.  The RSO must be an active participant along with the imaging department manager in an ongoing program that is designed to prevent personnel from receiving anywhere near the maximum allowed exposures. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 55  Radiation Hormesis  There are numerous studies that suggest a potential radiation hormesis effect, which is a beneficial consequence of radiation for populations continuously exposed to moderately high levels of radiation, exists.  During the course of human evolution over millions of years, advantageous genetic mutations caused by radiation exposure may have occurred, resembling those that allow lower animals today to demonstrate radiation hormesis. Therefore, to assume risk from very small amounts of radiation exposure (two or three times normal background levels) may be incorrect.  Until the radiation hormesis theory is proven, the medical radiation industry will continue to follow the principle of ALARA for radiation protection purposes. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 56  Occupational and Nonoccupational Dose Limits  EfD limits for radiation workers and the population as a whole  For the protection of radiation workers and the population as a whole, EfD limits have been established as guidelines.  The annual upper boundary limits are designed to limit the stochastic (probabilistic) effects of radiation.  The annual upper boundary limits take into account the EqD in all radiation-sensitive organs found in the body. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 57 Occupational and Nonoccupational Dose Limits (Cont.)  Special limits for selected areas  Because the WT factors used for calculating EfD are so small for some organs, an organ that is associated with a low WT factor may receive an unreasonably large dose, whereas the EfD remains within the allowable total limit.  To prevent deterministic effects, special limits are set for the crystalline lens of the eye and localized areas of the skin, hands, and feet. Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 58  Occupational And Nonoccupational Dose Limits Copyright © 2014 by Mosby, an imprint of Elsevier Inc. 59