Limits For Exposure To Ionizing Radiation

RADL 70

Kyle Thornton

A Little Background

• Wilhelm Conrad Roentgen discovered x-rays in 1895

• In 1896, Henri Becquerel observed rays coming from a uranium containing substance

• In 1898, Pierre and Marie Curie discovered radium

More Background

• Becquerel noticed a skin reaction (erythema) 2 weeks after carrying radium in his pocket

• In 1896, hair loss was also noted from radiation exposure

• Pierre Curie exposed areas of his own skin to radium to observe the results

• The first fatality connected with radiation exposure was Clarence Daly who worked for Thomas Edison

A Little More Background

• The first safe dose was established in 1902 as 7 minutes to prevent erythema

• Shielding was rarely used• Equipment operators would demonstrate by

exposing themselves to the beam to prove it didn’t hurt

• As a consequence, early radiologists often had multiple amputations of fingers and an increased incidence of leukemia

Skin Erythema Dose

• The skin erythema dose was the unit under which there would be a negligible risk of developing erythema

• It was determined that different individuals were either less or more sensitive to radiation, therefore were more or less inclined to develop erythema

• The Roentgen was formally adopted in 1928

Organizations That Derive Standards

• UNSCEAR, BEIR– Research and report

• ICRP, NCRP, CRCPD– Report, make recommendations

• State and federal regulations, NRC, FDA, EPA, OSHA– Regulatory agencies

UNSCEAR – United Nations Scientific Committee on Effects of Atomic

Radiation• Established in 1955

• Assesses and reports on exposures to humans and the environment to ionizing radiation from natural sources, man-made practices, and accidental releases

• Findings are based on epidemiological and research findings

BEIR – National Academy of Sciences, National Research Council Committee on the

Biological Effects of Ionizing Radiation

• Advisory group to UNSCEAR

• Reviews studies of effects of ionizing radiation on humans

• Formulates reports

ICRP – International Council on Radiological Protection

• Formed in 1928• Considered to be the international authority

on the safe use of sources of ionizing radiation

• Makes recommendations to regulatory agencies based on reports from agencies such as BEIR and UNSCEAR

• Not a regulatory agency

NCRP – National Council on Radiation Protection and Measurement

• A national organization that reviews recommendations from ICRP

• Publishes reports• Not an enforcement agency, makes

recommendations• Many recommendations from this agency

are used as national radiation protection standards

CRCPD – Conference of Radiation Control Program Directors

• Established in 1968 – made up of individuals in state and local government who regulate and control the use of radiation sources

• Developed the Suggested State Regulations for Control of Radiation

Regulatory Agencies

• U.S. Nuclear Regulatory Commission (NRC)• Agreement states – 29 members, California is one

of them• U.S. Environmental Protection Agency (EPA)• U.S. Food and Drug Administration (FDA)• U.S. Occupational Safety and Health

Administration (OSHA)

NRC

• Established in the 1940’s as the U.S. Atomic Energy Commission

• Has the power to enforce radiation protection standards

• Does not regulate or inspect diagnostic imaging facilities

• Oversees the nuclear energy industry• Publishes rules and regulations in Title 10 of U.S.

Code of Federal Regulations

Agreement State

• States that have had the authority to regulate transferred to them by the NRC

• Before transfer can occur, it must be determined that the state’s radiation safety program is compatible with that of the NRC– Must protect public health and safety

EPA

• Established by the executive branch in 1970

• Oversees general area of environmental monitoring

• Provides citations for non-compliance

FDA

• Regulates the design and manufacture of electronic products by virtue of the Radiation Control Health and Safety Act of 1968

• Inspects diagnostic x-ray equipment

• Establishes specific operational standards for x-ray equipment

OSHA

• A monitoring agency in places of employment, mostly in industry

• Regulates occupational exposure to radiation

• Oversees regulations for training programs

• Oversees “right to know” regulations

State Licensure Requirements

• A voluntary process designed to ensure safe operation of radiologic equipment

• As many as half of the operators of radiologic equipment in the U.S. are not certified

• Most studies have proved that licensed operators provide better radiation protection

• The goal is to ensure that operators meet minimum safety standards thereby delivering quality patient care

Radiation Safety Officers and Medical Physicists

• A designated person in an institution approved by the NRC and the state

• Ensures that accepted guidelines for radiation protection are observed and practiced in that institution

• Responsible for the formation of the institutional Radiation Safety Program

Effective Dose Equivalent Limiting System

• Current method for assessing radiation exposure and associated risk to radiation workers and the general public

• The threshold dose that results in a negligible risk of bodily injury or genetic damage

Radiation Control Health and Safety Act of 1968 – Public Law

90-602• Enacted to protect the public from the hazards of

unnecessary radiation exposure from electronic equipment– Includes microwave ovens, color TV’s and diagnostic

x-ray equipment

• Falls under the jurisdiction of the FDA• Includes minimum standards for the manufacture,

installation, assembly, and maintenance of machines used for radiologic procedures

Code of Standards for X-Ray Equipment Since August 1, 1974• Positive beam limitation• Minimal permanent filtration• Exposure reproducibility and linearity• Beam limitation devices for fluoroscopic

spot films• Presence of beam-on indicators• Inclusion of manual backup timers for AEC

should the phototimer fail

Consumer-Patient Radiation Health and Safety Act of 1981 – Title 9 of Public

Law 97-35• Established minimal standards for accreditation of

educational programs for persons who administer radiologic procedures– and

• The certification of such persons• This was to ensure that medical/dental procedures

are consistent with safety precautions and standards

• No penalty exists for state non-compliance

Non-Stochastic Effects

• Deterministic effects• There is a threshold dose for these effects• Early effects – erythema, decreased WBC

count, epilation• Early serious effects – hematopoietic

syndrome, GI syndrome, cerebrovascular syndrome– Acute radiation syndrome

Non-Stochastic Effects

• Late effects– Cataracts– Fibrosis– Organ atrophy– Reduced fertility– Sterility– Loss of parenchymal cells

Stochastic Effects

• Non-threshold, randomly occurring effects

• Includes cancer, and genetic effects

NCRP Recommendations

• TEDE – Total effective dose equivalent– 5 rem annually (50 mSv)

• TED – Lifetime total effective dose– Should not exceed 10 mSv or 1 rem times that

person’s age

Radiation Hormesis

• A beneficial consequence of constant exposure to radiation exposure

• Based on information from many studies• Follows lower-life form animals• Radiation induced mutations that are

advantageous have occurred, i.e., lower incidence of cancer than that of the general population

Evolution Of Occupational Exposure Limits

NCRP’s Recommendations For Exposure Limitations