Keywords

FormalPara Objectives:
  1. 1.

    Understand the difference between nonionizing and ionizing radiation.

  2. 2.

    Understand the difference between stochastic and non-stochastic effects.

  3. 3.

    Be able to discuss the concept of ALARA.

Everyone is concerned about patient radiation dose. From 1993 through 2008, radiation dose attributed to medical radiation rose from 0.54 to 3 mSv per capita. The largest component of the medical patient radiation dose was CT scanning (49%). This is despite the fact that CT scanning makes up only 17% of the total medical procedures that contributes to a patient’s radiation dose.

The radiation dose for all diagnostic exams should be minimized to the lowest amount of radiation needed to produce a diagnostic quality exam [1].

What Is Radiation?

Radiation is emitted from unstable atoms. Unstable atoms are said to be “radioactive” because they release energy (radiation). The radiation emitted may be electromagnetic energy (x-rays and gamma rays) or particles such as alpha or beta particles. Radiation can also be produced by high-voltage devices, such as x-ray machines. X-rays are a form of electromagnetic energy with a wavelength that places it into an ionizing radiation category. In a diagnostic exam, these photons can penetrate the body and are recorded on digital or film medium to produce an image of various densities that show details inside the body.

Light, radio, and microwaves are nonionizing types of electromagnetic radiation. Radio waves are used to generate MR images. X-rays and gamma rays are ionizing forms of electromagnetic radiation and can produce charged particles (ions) in matter. When ionizations occur in tissue, they can lead to cellular damage. Most damage is repaired by natural processes. In some cases, the damage cannot be repaired or is not repaired correctly which can lead to biological effects.

There are two categories of biological effects related to radiation exposure:

  • Non-stochastic (also called deterministic)

  • Stochastic (also called probabilistic)

  • Non-stochastic effects can occur when the amount of radiation energy imparted to tissue (dose) exceeds a threshold value. Below the threshold, no effect is observed. Above the threshold, the effect is certain.

    Examples:

    • Skin injury

    • Cataracts

  • Stochastic effects can manifest at any dose, meaning there is no threshold below which the effect cannot occur. In reality, the probability of a stochastic effect increases as radiation dose imparted to the tissue increases.

    Examples:

    • Cancer

    • Leukemia

Where Do We Use Radiation in a Hospital?

  • Radiography:

    • Fluoroscopy

    • Mammography

    • Cardiac catheterization

    • Computed tomography

    • Radiation therapy (linear accelerator)

  • Radioactive material:

    • Nuclear medicine

    • Radiation therapy

Listed below are three tables – they provide an estimate of effective radiation dose from common diagnostic exams and interventional procedures (Tables 2.1, 2.2, and 2.3). As a reference standard, the average annual background radiation we all receive from the sun and soil is 3 mSv.

Table 2.1 Typical effective radiation dose from diagnostic x-ray-single exposure
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Table 2.2 The dose a patient could receive if undergoing an entire procedure that may be diagnostic or interventional. For example, a lumbar spine series usually consists of five x-ray exams
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Table 2.3 Typical effective radiation dose from nuclear medicine examinations
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What Are the Risks?

There is no threshold for stochastic effects so any imaging procedure or therapy that involves the use of radiation involves some risk. When performed properly, the risk is usually very small and is far outweighed by the medical benefit of having the procedure. Regardless, the concept of ALARA (keeping the radiation dose as low as reasonably achievable) should always be employed to minimize the risk.

A small percentage of imaging and therapy studies performed in the hospital can potentially exceed threshold values for non-stochastic effects.

Radiation therapy and interventional fluoroscopy procedures may result in radiation doses that exceed the threshold dose for skin injuries, and less frequently for cataract induction. The procedures performed in these areas are often lifesaving, and every effort to minimize the magnitude of these effects is taken.

Resources

As you continue your career in medicine, you will specialize. Part of medicine, in virtually all areas of specialization, involves ordering x-rays or nuclear medicine based procedures for your patients.

In the news media, great attention has been paid to the increase in medical radiation dose to members of the public. Currently, there are discussions and debates over the appropriateness of ordering certain exams without need. This will become a health system financial restraint (CMS’ QPLE/AUC program) as well as a public health question.

Some Resources to Look into:

  • S: Ionizing radiation is the first thing we think about when we think about safety in imaging. In addition to radiologists, cardiologists, orthopedic surgeons, emergency physicians, podiatrists as well as medical professionals with office “x-ray” machines need radiation safety education and support. Know about and use these resources such as your health physicists.

  • A:    Resources such as health physicists, radiologists, ACR Appropriateness Criteria™, Image Gently™, Image Wisely™, and Choosing Wisely™ will help you to order appropriate studies while managing resources and maximizing safety.

  • F: Be aware that your imaging specialists are using techniques such as collimation of the examined area, reducing fluoroscopy time, and selecting appropriate number of images to answer the clinical question asked.

  • E: Resources such as health physicists and radiologists can help to advise and manage inappropriate or excessive radiation exposure to patients such as pediatric and pregnant patients. The ALARA principle is key to the SAFE use of ionizing radiation and, as we shall see, other imaging modalities such as MRI and ultrasound.