Radiation Exposure Quality Assurance

This article navigates the reader through the rational for a high suspicion for spinal cord injury in the trauma patient. This lesson gives clear explanations of the plain film diagnostic imaging criteria, CT protocols, and is truly a treatise in horizontal beam imaging.

Author: Nicholas Joseph, Jr. R.T (R)(CT)
Credits: 0.1

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The purpose of this module is to discuss how an X-ray quality assurance program is administered in a manner that reduces unnecessary patient dose and provides ongoing evaluation of procedures to reduce occupational exposure. The overall designed of a comprehensive quality control program should include review and updates of administrative x-ray procedures, education of employees’ not just technologists, and preventive maintenance methods. X-ray quality control involves continued evaluation of adequacy and effectiveness of multi-modality use of ionizing radiations, and ongoing corrective measures when identified.

At the heart of any quality control program is embracement to the principle of (ALARA) as low as reasonably achievable patient dose. Having commitment to ALARA by radiologists, technologists, and all healthcare providers is truly the first step to reducing the collective doses within in a radiology department. This is also a responsibility of the radiation safety officer (RSO) of the institution. The concept of ALARA is not new, it has been in practice for more than 3 decades; surprisingly, many technologists do not know that it is based on federal mandates. This includes written policies, instructions, and procedures that foster ALARA mandates as managed by the RSO. Institutions will from time to time add new procedures, change imaging protocols, purchase new innovative equipment, hire new employees, etc so that evaluation of procedures, doses, and policies are ongoing. Keep in mind that institutional radiation dose sums goals are consistent with individual dose goal of being as low as is reasonably achievable. Maintaining institutional dose sums as low are is reasonable is true for each individual as well as the sum of the individuals.

What is radiation and ionizing radiation?

Not all members of the medical community are aware of what is ionizing radiation and why we are so particular about keeping dose low. There are two forms of radiation we are concerned about in imaging: electromagnetic radiation (EM) and particulate radiation. In the simplest of terms electromagnetic radiation is a packet of energy in the form of electromagnetic waves. Most people have heard of the various types of radiations: radio waves, microwaves, ultraviolet light, gamma rays, and x-rays of course. Visible light is also a form of radiation and is visible to the human eye. All other forms of electromagnetic radiations are invisible to the human eye and require special instruments to detect them. Particulate radiation is a fast moving particle derived from an atom. Fast electrons, fast neutrons, and protons can be forms of particulate radiation. Particulate radiations have a small mass whereas electromagnetic radiation contains no mass.

Radiations occur as non-ionizing or ionizing radiations. Radiation that can move an atom or its parts or cause them to vibrate, but do not have sufficient energy to remove an electron, are called non-ionizing radiations. Examples of non-ionizing radiation are sound waves, visible light, and microwaves. We take advantage of non-ionizing radiations to broadcast information in the form of radio waves. We use microwaves to heat food and in telecommunication. Infrared radiation is used to create heat, and visible light to illuminate our homes. As you can see there are many uses for non-ionizing radiation as it is considered harmless radiation when properly used.

Ionizing radiation describes radiation that contains enough energy to remove electrons from an atom or molecule during an interaction creating ions. The term ionization means that an atom or molecule has lost an electron and is ionized. Ionizing radiations that can pass through matter are called penetrating radiations. X-rays and gamma rays are used medically because they can penetrate the human body and be detected. This is how we get medical information in the form of images useful for diagnosis of diseases. Penetrating ionizing radiation is also used to treat some disease states such as tumors and kill cancer cells. Just as penetrating ionizing radiations can cause damage to tumors and cancer cells, it can cause damage to normal human tissues. Other useful benefits of ionizing radiation include generating electric power and killing bacteria during manufacturing processes. Limiting potential damage to cells is the rationale for taking precautions when administering ionizing radiation to diagnose or treat disease or when working with it.

Radiation Terms and Units

Radiation does have a biological affect on humans although it is invisible. Therefore, we must be able to measure its presence and to relate the amount of radiation the body receives to its physiological effects. To do this we use two concepts, exposure and dose. In the simplest terms, when you are exposed to radiation the body absorbs a portion of it receiving a dose. Radiation terms and units of measurements are possible because ionizing radiation is detectable and measurable using specialized instruments. The most common way to express radiation is to use a universal nomenclature called the international System of Units (SI). Conventional units of radiation measurement are the: roentgen, rad (radiation absorbed dose), and rem (radiation equivalent man). It is proper to refer to radiation units by their universal nomenclature or system international (SI) units. SI units of radiation are the gray (Gy), roentgen in C/kg, and sievert (Sv).

The “roentgen” is the amount of ionization of atoms in air produced by radiation. The roentgen is a unit of radiation exposure that is the amount of radiation moving through air. The roentgen is measured in coulomb/kilogram (C/Kg). In SI units the unit of exposure in air is expressed as C/Kg. The roentgen can be thought of as a quantity of ionizing radiation as it moves through air. For example the roentgen quantifies exposure, or quantity of radiation such as x-rays moving through air before they reach the part that is being “x-rayed.” Once radiation reaches the patient a small amount of it will be absorbed as it passes through the exposed part. The roentgen only applies to electromagnetic radiations such as x-rays and gamma rays. Exposure to particulate radiations (alpha or beta particles) is not expressed in roentgens. The roentgen is a measure the energy produced by gamma radiation in a cubic centimeter of air. The abbreviation for the roentgen is the capital letter “R.”

The amount of radiation that is absorbed, or does not exit the patient is called the radiation absorbed dose (rad). As stated before, the rad is a conventional unit; however, the proper unit is the SI unit of absorbed dose, which is the gray (Gy). These units are often related through their conversion factor of 1Gy = 100 rad.

The Roentgen Equivalent Man (rem) is a unit that relates the absorbed dose of any type of radiation to the effectiveness of biological effects. To do this a conversion factor called a “quality factor” is multiplied times the dose in rad to get the dose in rems. Keep in mind that the United States National Institute of Standards and Technology “strongly” discourages the use of the term rem. The proper term is the sievert (Sv), which is the SI unit of dose equivalence. The conversion from rem to Sv is 1 rem = 0.01 Sv = 10 mSv. The standard international unit sievert is defined as 1 Sv = 1 J/kg. From a practical use as in radiation safety, the units of exposure, dose, and radiobiological equivalent are acceptably used interchangeably despite their different scientific definitions.

Radioisotopes are commonly used in medicine to provide functional and anatomical information. These materials are radioactive, meaning they decay and give off ionizing radiations. The amount of radioactivity in these materials decreases over time as a result of radioactive decay. The number of disintegrations the radioisotope material undergoes is a measure of its activity. The amount of time it takes for a material to lose half of its radioactivity is called its half-life. Different types of radioisotopes will have different half-lives ranging from fractions of a second to thousands of years. The period of time that it takes for a material to lose one half of its radioactivity is called its half-life. The half-life for different radioactive materials varies from fractions of a second to thousands of years. The conventional unit of activity is the curie, whereas 1 curie = 37 billion disintegrations per second. The SI unit of activity is the Becquerel (1 Becquerel is equal to 1 disintegration per second).

Table of Common Radiation Units
Quantity Measured Old Unit SI Unit Conversion
Exposure Roentgen (R) Coulomb/Kg (C/kg) 1 R = 2.58 x 10-4C/kg
Dose (absorbed) Rad Gray (Gy) 1 Rad = 0.01 Gy = 10 mGy
Dose (radiological equivalent) Rem Sievert (Sv) 1 Rem = 0.01 Sv = 10 mSv
Activity (radioactive material) Curie (Ci) Baquerel (Bq) 1 mCi = 37 GBq

While most laypersons and medical professionals are concerned about medical radiation exposure, it is important to realize that radiation exposure is all around us in the form of what is called background radiation. Background or environmental radiation dose is considered low. Forms of background radiation include cosmic radiation, terrestrial radiation (from the ground and rocks), and radioactive materials such as radon gas. Trace amounts of radioactive elements such as uranium and thorium can be found in rock such as granite and limestone. As these rocks erode due to rain radioactive particles wash into the soil and ground water. They also produce two airborne radioactive gases, radon and thoron. Being in air they are dispersed enviromentally and weathered to where the concentration is low. Airborne radioactive particles can increase in areas where the concentration is high and the buildings are poorly ventilated. For most of the population most radiation exposure is from radon. Nationally it account for about 55% of human exposure in the United States. Radon exposure varies from almost none in the San Juan Islands to about 1,475 mrem/year around the Spokane, Washington area. The central concern with radon inhalation is lung cancer. Studies on miners have demonstrated an increased risk; however, exposure to normal residential levels are less conclusive. In areas with high average levels of radon, home testing is highly recommended.

This pie chart shows the relative percentage of radiation dose on the U.S. population. Approximately 55% comes from radon, another 15% from external sources such as cosmic radiation, 11% from internal sources, 15% medical, 3% consumer, and 1% other sources.

The amount of background radiation one gets varies depending on a number of factors. For example, altitude above sea level, building materials, construction and ventilation, and underlying rock formations can effect annual dose. The average annual individual effective dose equivalent received in the United States is about 3 mSv (360 mrem). Annual doses on other contienents may vary due to lattitude change and geographical make-up of the earth.

Estimated Individual Average Annual Effective Dose in United States
Source mSv mrem
Inhaled (radioactive particles, e.g. radon 2 200
Terrestrial Radiation 0.28 28
Cosmic radiation 0.27 27
Other Internally Deposited Radionuclides 0.39 39
Rounded Totals From All Sources 3 300

About 15% of human radiation exposure is due to medical use. Those who request medical imaging procedures for diagnosis and/or treatment of disease must balance the risk associated with each procedure with the benefit derived for the patient. Professionals who administer a dose of ionizing radiation for the treatment of disease or for diagnostic purposes balance exposure and the need for As Low as Reasonably Achievable to get good diagnostic or treatment quality results. This can be accomplished by assuring each practitioner or operator of radiologic equipment is properly educated and qualified through continuing education. ALARA is assurred by maintaining updated technique charts for each type of equipment used. Modern radiography may use updated digital programs that coorelate exposure, image noise and digital image display factors to reduce patient dose.

Medical sources of Ionizing Radiations

Medical radiation exposure is the largest source of man-made-radiation in the United States. It accounts for about 15% of human exposure, which is why we are concerned about managing its risks and benefits. Medical radiation exposure comes from many sources that include x-ray machines and radioactive materials commonly used in the diagnosis and treatment of diseases. There are various types of x-ray machines varying from stationary units to mobile (portable) units. Real time imaging machines called fluoroscopes can also be stationary or mobile {C-arms). Within recent years various types of computed tomography CT) scanners have been added to our medical arsenal to diagnose and treat diseases. Nuclear medicine relies on various radioactive materials (capsules, liquids, or gases) used in diagnostic procedures. Recent addition of positron emission tomography (PET) scanners has added the need for high energy gamma radiation emitters to the list. Radioactive materials are also used in the laboratory to perform “in-vitro” or test-tube testing on blood, urine, or cells.

Radiation therapy uses high energy radiations to shrink tumors and treat various medical conditions like cancer. Radiation used for therapeutic purpose involves equipment like linear accelerators, teletherapy machines, and radioactive sources such as sealed implant containers, and radioactive drugs or brachytherapy implants. Some of these sources may pose a risk to radiation workers, visitors, and family members. As a consequence some patients who receive a source dose may be confined to a special room until the half-life of the material is within acceptable limits. All sources of medical radiation use are managed in a radiation quality assurance program. Some radiation doses from standard imaging exams and procedures are listed in the table below.

Standard Medical Exams and Dose
Sample Types of Medical Exposure Dose in mrem Dose in rem
Chest X-ray 15 0.015
Dental x-ray (3 inch diameter) 300 0.300
Spine x-ray plain films 300 0.300
Thyroid uptake scan 28 (to thyroid) 0.28
Thyroid oblation 18,000 (to thyroid) 18

Standard Medical Exams and Dose
Exam Effective Dose mSv (mrem)1 Exam Effective Dose mSv (mrem)2
Chest (AP) 0.02 (2) Mammogram 0.7 (70)
Chest (LAT) 0.04 (4) Dental (panoramic) 0.09 (9)
Pelvis (AP) 0.7 (70) DEXA (whole body) 0.0004 (0.04)
Thoracic Spine (AP) 0.4 (40) Hand/Foot 0.005 (0.5)
Lumbar Spine (AP) 0.7 (70) Abdomen 1.2 (120)

Complete X-ray Exams and Dose
X-ray study Effective Dose mSv (mrem)1
Barium Enema (10 images, 135 sec. fluoroscopy) 7.0 (700)
Barium Swallow (24 images, 106 sec. fluoroscopy) 1.5 (150)
CT head 2 (200)
CT abdomen 10 (1,000)
Angio (heart study) 7.5 (750) – 57.0 (5,700) 3
Coronary Angiogram 4.6 (460) – 15.8 (1,580)3

Acute Radiation Exposure

Acute radiation exposure is an exposure to a single large dose or a series of moderate doses in a short time frame. Large acute doses can occur from an accidental or emergency exposure in a medical setting, for example, radiation therapy or angiography fluoroscopy procedure. Excessive direct nuclear radiation exposure to humans causes cancer, gene mutation and radiation sickness. Radiation sickness include effects like nausea, vomiting, diarrhea, weakness, hair loss, skin burns, reduced organ function, premature aging and even death. High exposures like those at the Fukushima plant do not occur in a medical setting since medical radiation doses are prescribed and have inherent limits. Medical radiation doses are generally to a local area such as to the breast and not to the whole body. As such, radiation doses in medicine are based on a benefit to the patient vs. risk of cell injury. We will talk more about the risk-benefit factors later. What is important is that we realize acute radiation exposure from medical radiation is not in the same dose range as acute radiation exposure from industrial source like a nuclear reactor.

Recent interest in acute radiation exposure has been renewed because of the nuclear emergencies caused by nuclear reactors at the Fukushima Daiichi nuclear power plant. Radiation level following the earthquake and tsunami and explosions at the plant rose to greater than 1,000 mSv/hour settling to about 400 mSv/hour or about 20,000 chest x-rays per hour. Water puddles with radiation levels upwards to 10,000 times normal limits were discovered when two workers stepped in them and received radiation burns. This prompted the Japanese government to call the U.S. Nuclear Regulatory Commission (NRC) and the IAEA for help to stabilize these reactors. Within hours radiation from the reactors was detected in Tokyo some 175 miles away. Radiation workers were unable to enter the reactors to affect repair until the dose dropped to below10 mSv/hr, which is about the dose received from 1 CT scan per hour. High accidental doses like these are not possible from medical radiation use. We should review the difference between medical radiation exposure and large dose accidental exposures such as the Fukushima disaster.

Acute radiation exposure is not the same as acute radiation syndrome (ARS). Acute radiation syndrome is also called radiation poisoning, radiation toxicity, or radiation sickness. Acute radiation exposure can occur to a local area of the body or whole body depending on the mechanism of exposure. Acute radiation exposure when it happens medically usually involves a small area of the body. Acute radiation exposure like at the Fukushima disaster involves the whole body and the dose is extremely large. Acute radiation syndrome does not and cannot occur from the exposure encountered in medical care. Acute radiation exposure has been documented to occur from improper fluoroscopic technique in interventional radiography suites. Consider the exposure charts above. In order for ARS to occur the dose must exceed 100 rad (10 Gy) whole body exposure. This is only possible from accidents in nuclear weapon or nuclear energy occupations. It can also affect the general public should it get out of hand like the Fukushima Japan disaster. This is a very rare occurrence considering the three-mile island accident that occurred in Pennsylvania resulted in no one getting a significant radiation dose. Likewise, the Chernobyl accident in Russia to which the Fukushima accident is comparable resulted in only 30 people dying from radiation syndrome.

When humans are irradiated with a large dose of ionizing radiation to which a biological response occurs within a few months are said to have an early effect. Late effects may also occur assuming the acute dose does not result in death. Early effects are called deterministic because as the dose increases the response becomes more severe. In other words, there is a known threshold dose for each type of response. Early effects occur from a wide range of doses from about 5 rad whole body to 300 rad small field local exposure. Of particular importance is a dose of 100 rad or higher whole body exposure because it causes an early effect called acute radiation syndrome. Acute radiation syndrome is those series of event resulting from high level radiation exposure resulting in death within days or weeks. Again, ARS does not occur from medical exposure because the dose required to effect the syndrome is not possible in a medical setting. Diagnostic imaging exposures do not have sufficient intensity or quantity, and does not involve whole body exposure. Acute radiation syndrome is actually three separate syndromes called the manifest illness that have specific clinical responses for which they are named. They are: hematological, gastrointestinal (GI), and central nervous (CNS) syndromes. ARS has four distinct periods in the following order: 1) prodromal, 2) latent, 3) manifest illness (hematological, GI, CNS), and 4) death or recovery. If recovery from ARS occurs the individual then has an inherent risk of suffering late effects, which will be discussed later in this article.

Early Effects of Radiation Exposure and Dose
Effect Anatomic Site Minimum Dose (rad)
Death Whole body 100
Hematological depression Whole body 25
Skin erythema Small field (local) 200
Epilation Small field (local) 300
Chromosome abrration Whole body 5
Gonadal dysfunction Local tissue 10

The acute radiation syndrome is lethal but has three distinct periods that mark impending doom. The first period is the prodromal period, followed by a latent period, and last is the period of manifest illness (hematological, GI, central nervous/neuromuscular) based on the dose. The prodromal period is the immediate response to a high dose of whole body exposure. It may last a few hours to a few days, but is shortened as the dose increases. During the prodromal period the person may experience nausea, vomiting or diarrhea. This will be followed by a latent period in which there is no outward signs of radiation sickness and the individual may think they have recovered. Nothing could be further from the truth. In fact, biological and physiological changes are occurring subclinically that will manifest in a few weeks if the dose is between 100 and 500 rad. The latent period may not be distinct at doses large enough to produce CNS syndrome. At these doses the latent period may only last a few hours before a violent manifest illness appears.

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