A fundamental knowledge of radiation effects and safety is essential for any pain management specialist who performs fluoroscopically guided procedures. It is sobering to note that practitioners of fluoroscopy and radiography in the first half of the twentieth century had the highest incidence of cancer-related death among all physicians. Although a complete review of this topic is beyond the scope of this chapter, the following outlines some of the most important details of working in an x-ray environment. These include basic principles of radioactivity, potential adverse effects to patients and physicians, and preventive measures for maintaining effective radiation safety.

Radiation is the process by which energy in the form of waves or particles is emitted from a source. Electromagnetic radiation (EMR) has no mass and no charge. Common types of EMR include gamma rays, x-rays, ultraviolet visible light, infrared, radar, microwaves, and radio waves. This list is in order of increasing wavelength.

X-rays are one of the most common potential radiation hazards in health care. The hazard is mainly due to potential harmful biological effects resulting from x-rays passing through matter with enough energy to remove electrons (ionizing radiation) from atoms, which can result in ionized atoms and free radicals (atoms with an unpaired electron in the outer shell). This risk of biological damage from radiation exposure can exist even with low doses. Biological effects of radiation exposure depend on two major factors: dose and duration. Greater exposure is associated with greater risk.

Radiation is both naturally occurring and man-made. It occurs all around us and cannot be completely avoided (“background” radiation.) We are also exposed to radiation through medically necessary testing (e.g., dental x-rays, nuclear medicine, and radiology procedures). Typically, the average individual is exposed to roughly 3.6 mSv per year or 360 mrem per year (see terminology in following section), of which 15% is due to medically necessary procedures.

Exposure (E) is the ability of energy to ionize air (source-related). The unit is the roentgen (R), which is the amount of radiation that produces ionization of one electrostatic unit (ESU) of either positive or negative charge per cc of air at 0°C and 760 mm Hg (STP). In SI units, it is coulombs (C)/kg (1R = 2.58 × 10).

Absorbed Dose (D) is a measure of the energy absorbed in a unit mass of material from radiation. It depends on the characteristics of the absorbing medium. The unit is the radiation absorbed dose or the rad (1 rad = 100 erg/g absorber). In SI units, gray (Gy) is the unit of radiation absorbed dose and is given by 1 Gy = 100 rad = 1 J/kg absorber. D = f × E (is the f-factor or roentgen-to-rad conversion factor). At diagnostic x-ray energies, the f-factor for air and soft tissues is close to 1.

Dose Equivalent (DE) is a measure of the biological damage that is likely to result from the absorbed energy. The unit is roentgen equivalents man, or rem. In SI units, the Sievert (Sv) is the unit of dose equivalent and is given by 1 Sv = 100 rem.

QF is the quality factor and related to linear energy transfer (LET) of the radiation in a given medium. It represents the effectiveness of the radiation to cause biologic or chemical damage. For pain specialists, it is important to note that the QF of x-ray is roughly equivalent to 1.0 such that rad × QF = rem. Moreover, 1R ≅ 1rad ≅ 1rem.

N is the modifying factor of the radiation and related to absorption coefficient of the absorbing material (assumed to be unity).

LET is defined as the amount of energy deposited per unit length of the path by the radiation and is measured in kiloelectron volts per micrometer. LET is proportional to the square of the particle charge and is universally related to particle kinetic energy. LET is the measure of the effectiveness of a particular radiation to cause biological damage. X-rays are considered low LET radiation.

Time is the amount of time a worker is exposed to radiation. (This should be as short as possible.)

Distance is the distance from the source (should be as far as practicable.)

Inverse Square Law is radiation exposure that varies inversely as the square of the distance. Therefore, if the distance from the source is doubled, the exposure rate is reduced by one-fourth.

Shielding is the use of appropriate materials to diminish exposure from a given source. Designing shielding for radiation protection must take into account the half-value layer (HVL), which is defined as the amount of shielding that reduces exposure from a radiation source by half. HVL is dependent on both the energy of the radiation and the atomic number of the absorbing material.

As a rough guideline using x-rays or fluoroscopy for the clinician, the units rad and rem are approximately equivalent (e.g., interchangeable). Rad refers to the radiation dose of the incident beam delivered to the air (i.e., what is coming) out of the fluoroscopy machine. Rem refers to the radiation dose (energy) deposited inside the patient and more closely reflects potential biological damage.

Scatter radiation is essentially any radiation other than the direct incident beam that comes out of the fluoroscopy machine.

The absorption of energy from radiation in living matter may lead to molecular excitation, releasing significant amounts of energy that is capable of breaking strong chemical bonds. Ionizing radiation is generally classified as either particulate (e.g., protons, alpha particles) or electromagnetic (e.g., x-rays, gamma rays). X-rays are generally produced in an electrical device that accelerates electrons from a cathode to high energy and then stops them abruptly in a target (e.g., tungsten-anode). Part of the kinetic energy of the electrons is converted into x-rays.

The process by which x-ray photons are absorbed depends on the energy of the particular photons and the chemical composition of the absorbing material. Two major processes occur for photon energies commonly used in diagnostic radiology: the Compton process and the photoelectric process. Each of these causes a transfer of energy from photon to electron. In this way, a mark is made that can ultimately serve as an image. It is also important to note that scattered radiation from the Compton process and the photoelectric effect are responsible for inducing untoward side effects and therefore require the practitioner to wear special equipment for protection.

X-rays are scattered by the atoms of patients, leading to scattered radiation. No amount of radiation can be considered safe for living matter. The maximum permissible dose (MPD) is the upper limit of radiation dose that one should be “allowed” to receive. Radiation exposure below this level probably only carries remote chances of clinically significant adverse effects.

The radiation dose from an average chest x-ray is approximately 10 to 20 mrad compared with 300 mrad for an average 2-second fluoroscopy scan. Whole-body total radiation dose exceeding 1 Sv (100 rem) can lead to problems that often first affect the most rapidly multiplying cells such as mucosa, bone marrow, and skin. Common radiation-related illnesses include radiation sickness, nausea, fatigue, hematopoietic disturbances, intestinal problems, alopecia, cataracts, and radiation dermatitis. The International Commission on Radiological Protection has determined that the risk of death from radiation-induced cancers or hereditary disorders of radiation is roughly 1/100 per sievert (100 rems) absorbed.

Since actively dividing cells are particularly affected by radiation, fetuses are at special risk. It is suggested that, except in emergencies, women of reproductive capacity should be x-rayed only in the first 10 days of their menstrual cycles (i.e., before ovulation has occurred—the 10-day rule). It may be most prudent to display warnings about risk to pregnancy for female patients and clinicians.