Radiation Safety

chapter 3 Radiation Safety



CHAPTER OUTLINE


Hazards of Ionizing Radiation

Maximum Permissible Dose

Patient Exposure

Personnel Monitoring Devices

Practical Application of Radiation Safety


OBJECTIVES


Upon completion of this chapter, the reader should be able to do the following:


• List the tissues most sensitive to radiation-induced damage

• State which personnel are prohibited from assisting in radiographic procedures

• State the two types of tissue damage that can occur from exposure to radiation

• Define maximum permissible dose (MPD) and name the organization that is responsible for setting dose limits

• List and define the units of radiation exposure for absorption

• State the MPD for occupationally exposed personnel

• List and describe the three types of personal exposure dosimeters

• State the three primary methods by which personnel are exposed to radiation during radiography

• List the practical methods that personnel can use to reduce personal exposure during radiography

• State the proper maintenance protocol for protective apparel

• State the risks and safety measures necessary with the use of fluoroscopy


GLOSSARY


Absorbed dose: The quantity of energy imparted by ionizing radiations to matter.


Dose equivalent: The quantity obtained by multiplying the absorbed dose in tissue by the quality factor.


Dosimeter: A device used to measure radiation exposure to personnel.


Dosimetry: Various methods used to measure radiation exposure to personnel.


Film badge: A method of dosimetry consisting of a plastic holder with a radiation-sensitive film in a lightproof package.


Fluoroscopy: A special radiographic diagnostic method in which a “live view” of the internal anatomy is possible.


Genetic damage: Effects of radiation that occur to the genes of reproductive cells.


Gray (Gy): The unit of absorbed dose imparted by ionizing radiations to matter (1 gray equals 100 rad).


Hemopoietic: Anatomic areas where red blood cells are produced.


Leukopoietic: Anatomic areas where white blood cells are produced.


Maximum permissible dose (MPD): The maximum dose of radiation a person may receive in a given time period.


Pocket ionization chamber: A method of dosimetry consisting of a charged ion chamber and electrometer, which can be read immediately to determine the amount of exposure.


Primary beam: The path that the x-rays follow as they leave the tube.


Secondary radiation: Commonly called scatter radiation, it is caused by interaction of the primary beam with objects in its path.


Sievert (Sv): The dose of radiation equivalent to the absorbed dose in tissue (1 sievert equals 100 rem).


Somatic damage: Damage to the body induced by radiation that becomes manifest within the lifetime of the recipient.


Thermoluminescent dosimeter (TLD): A method of dosimetry consisting of a chamber containing special compounds that become electrically altered by ionizing radiation.



INTRODUCTION


During each laboratory or diagnostic procedure, safety should be a primary objective. Radiography is no different.


It is a scientific fact that ionizing radiation is hazardous. The exposure to stray radiation is a common occurrence with the use of diagnostic x-rays in veterinary medicine. However, following proper safety precautions can limit the exposure.


The veterinarian must establish and maintain a radiation safety program for the protection of the patient, the client, and the technical staff. Safe operating procedures for each facility should include (1) an adequate technique chart or comparable system, (2) positioning aids, (3) protective clothing and other protective barriers, (4) personnel dosimetry devices, (5) emergency procedures for malfunctioning x-ray equipment, and (6) quality control measurements and tests.


All radiographic equipment including radiation protection devices must meet state regulation requirements, which can vary by state. Regulations can usually be obtained from the state Department of Health.


The radiographer should keep one important concept about ionizing radiation in mind: Radiation should be respected … not feared.



HAZARDS OF IONIZING RADIATION


All living cells are susceptible to ionizing radiation damage. Affected cells may be damaged or killed. Cells that are most sensitive to radiation are rapidly dividing cells (e.g., growth cells, gonadal cells, neoplastic cells, and metabolically active cells). Therefore persons younger than 18 years of age and pregnant women should not be involved in radiographic procedures. Other tissues that are readily sensitive to radiation include bone, lymphatic, dermis, leukopoietic and hemopoietic (blood forming), and epithelial tissues.


A vast amount of knowledge has been collected over the years concerning the effects of radiation on the body. Two types of biologic damage can occur from overexposure to radiation: somatic damage and genetic damage.


Somatic damage describes damage to the body that becomes manifest within the lifetime of the recipient. Radiation can produce immediate changes in the cell, although the damage may not be apparent for some time. Because the body has the ability to repair itself, cell damage may never be appreciated or visible. Damage is more extensive when the body is exposed to a single massive dose of radiation than to smaller, cumulatively equivalent repeated exposures. As mentioned earlier, body cells are not equally sensitive to radiation, and the healing process varies among cell types. Examples of somatic damage include cancer, cataracts, aplastic anemia, and sterility.


Genetic damage from radiation occurs as a result of injury to the genes (DNA) of reproductive cells. Ionizing radiation can damage chromosomal material within any cell. The result of the damage is determined by the cell type (i.e., somatic cell or reproductive cell). Damage to reproductive cells can result in the effect known as gene mutation. Genetic damage is not detectable until future generations are produced. The offspring of irradiated persons may be abnormally formed because of changes in the hereditary material, resulting in alteration of the individual phenotype (physical appearance). The mutation may be lethal or may be only a visible anomaly. The gene mutation may also stay latent or recessive until the second or third generation.


Mortality from radiation is caused by exposure to extremely high levels of radiation. Exposure to a large, single dose of radiation, as from a hydrogen bomb, is necessary to cause rapid death. A single exposure to a dose of 300 rad (radiation absorbed dose; see later) or more has been shown to be lethal to humans. Further information on death due to radiation exposure can be found in a radiobiology textbook. A technologist working in a practical situation and following proper safety protocol should never receive this level of radiation. Because the body has the ability to repair itself, accumulative smaller doses of radiation are sublethal.


Theoretically, no amount of radiation is nondamaging. Even under the best conditions, some exposure to ionizing radiation will occur. Therefore it is the responsibility of radiographers to limit the exposure of ionizing radiation to patients, clients, and themselves. The exposure received by any individual should never exceed the maximum permissible dose.



MAXIMUM PERMISSIBLE DOSE


The maximum permissible dose (MPD) is of great interest to the radiographer. The MPD is the maximum dose of radiation that a person may receive in a given period. The concept of MPD was introduced to denote an amount of irradiation that does not involve a risk to the health of radiation workers so great that it significantly influences future generations or the individuals occupationally exposed. The MPD helps to determine whether procedures and equipment are adequate to provide the degree of protection necessary to stay within the stated limit.


The National Committee on Radiation Protection and Measurements (NCRP) defines the MPD for occupationally and nonoccupationally exposed persons. The NCRP is a nonprofit organization, chartered by Congress and consisting of scientific committees of persons who are experts in a particular area.


The NCRP has issued a practical approach to radiation safety in the workplace through a program known as ALARA (as low as reasonably achievable). The process of ensuring that radiation exposures are ALARA may be viewed as an ongoing series of decisions about possible radiation protection actions. A practical approach to the implementation of ALARA in a medical setting must provide a framework for a standard radiation protection program. Thus certain rules and regulations have been designed to achieve ALARA in the veterinary workplace.


The NCRP and most state health codes permit occupationally exposed persons to restrain and position animal patients manually for radiography when absolutely necessary. However, some states prohibit manual restraint of animals during diagnostic radiography by occupationally exposed personnel. In these cases the animal owner or staff personnel who are not routinely involved in radiographic procedures must be used for this purpose.


Another option customary in some states is the use of chemical restraint and positioning devices only (e.g., anesthesia, sandbags, adhesive tape).



Radiation Exposure Units


To quantify the amount of radiation received, radiation exposure units are stated in two categories: absorbed dose and dose equivalent.


1. Absorbed dose is the quantity of energy imparted by ionizing radiations to matter per unit mass of the matter. The unit of absorbed dose is the gray (Gy). This replaces the previously used unit, which is known as the rad (1 Gy = 100 rad).

2. Dose equivalent is the quantity obtained by multiplying the absorbed dose in tissue by the quality factor. This equation accounts for the differing biologic effectiveness of equal absorbed doses and other modifying factors. The unit of dose equivalent is the Sievert (Sv). The Sievert supersedes the rem, which was previously used for this purpose (1 Sv = 100 rem).

State and federal restrictions dictate that occupationally exposed individuals older than 18 years of age and wearing monitoring devices can receive up to 0.05Sv/year from occupational and background exposure.


Any person younger than age 18 is not allowed to enter the radiographic suite during exposure unless ordered by a medical doctor. These young people are still growing and are more susceptible to radiation damage. Nonoccupationally exposed persons can receive 10% of this figure (0.005Sv/year). The MPD for the general public is set at a much lower level because they will not be monitored and are not trained to recognize and avoid accidental exposure (Table 3-1).


TABLE 3-1 MAXIMUM PERMISSIBLE DOSE (PER CALENDAR YEAR)



















  OCCUPATIONALLY EXPOSED (>18 YR) NONOCCUPATIONALLY EXPOSED (>18 YR)
Whole body 0.05 Sv (5 rem) 0.005 Sv (0.5 rem)
Individual organs and tissues 0.5 Sv (50 rem) 0.05 Sv (5 rem)
Lens of the eye 0.15 Sv (1.5 rem) 0.03 Sv (3 rem)

Booklets that outline the specific requirements and regulations on radiation protection in veterinary medicine can be purchased from NCRP for a small fee.* Suggested readings include NCRP #36, Radiation Protection in Veterinary Medicine (also see Suggested Readings later).



Patient Exposure

Related posts:

  1. Radiographic Technique Evaluation
  2. Developing a Technique Chart
  3. Anatomy of the X-ray Machine
  4. Small Animal Forelimb

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May 27, 2016 | Posted by in ANIMAL RADIOLOGY | Comments Off on Radiation Safety

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