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Radiation Safety for Interventional Pain Physicians

Vikram B. Patel MD, DABA, FIPP, DABIPP

AIM Specialty Health, Chicago, IL, USA

Introduction

During interventional pain procedures, it is almost a standard of practice to use fluoroscopy or other imaging guidance [1]. Interventional pain physicians are therefore constantly exposed to radiation. It is crucial to understand the effects of radiation not only to the patient but also to the physician and support staff. Newer technologies such as CT-fluoroscopy may help reduce the radiation even further while providing better imaging of the skeletal components [2]. While using fluoroscopy, it is important to understand the effects of radiation on the human body, operation of the equipment and protection measures against radiation exposure. Proper training in the use of radiation equipment will reduce the level of radiation exposure [3].

History

X-ray was discovered by Wilhelm Roentgen in 1895. The first use of X-ray to visualize a metallic object in a human body was in 1896 [4]. In 1994, the US Food and Drug Administration (FDA) published an advisory following several reports of radiation injuries in patients undergoing fluoroscopic-guided procedures [5].

Types of Radiation

Radiation is defined as energy given off by matter in the form of rays or high-speed particles [6]. Radiation can be ionizing or non-ionizing depending on how it affects matter. Non-ionizing radiation is usually non-harmful. But ionizing radiation has more energy and can damage the matter. These include X-rays, cosmic rays etc. Figure 13.1 demonstrates the penetrating power of different types of radiation [6].

**Figure 13.1** Penetrating power of radiation [6].

Sources of Radiation Around Us

Radiation occurs in nature but can be man made. Figure 13.2 explains these radiation sources.

**Figure 13.2** Sources of radiation exposure in the United States [6].

Anatomic Effects of Radiation

Effects of radiation on human cells can be divided into four categories. It depends on the type and intensity (amount and duration) of radiation exposure.

No damage: Injured cell repairs itself.
- –Very low levels of radiation which may not be seen as tissue damage as the cells may not exhibit any damage. The small number of cell deaths will, in most cases, have no consequences. However, modifications in single cells such as genetic transformations may ultimately lead to malignancy and can have serious consequences [7].

Cell death: Cell is replaced by the body through the normal biologic process.
- –Higher levels of radiation damaged cells may be naturally replaced through a biologic process – e.g. superficial skin cell damage (dermatitis).

Cell death: Incorrect repair and physical damage.
- –Even higher levels of radiation may lead to cell death that is not only visible as damage but the biologic process fails to repair the damaged cell in the normal physiologic process leading to an outcome such as cancer or abnormal growth.

Cell death: No repair and cell death with organ failure.

Not all radiation energy is equal and the half-life of radiation decreases over time. Some substances such as Iodine-131 have half-life measured in days whereas some substances such as Uranium-238 have a half-life measured in billions of years [6].

The biologic effect of radiation depends on the total amount of exposure measured in time and intensity. By reducing either or both, the effects of radiation can be significantly reduced. The biologic effects also depend on how rapidly the dose is delivered and how concentrated it is over the body. The amount of radiation affecting the matter is measured as a “dose”. This dose is measured in rems.

Certain relevant terms are:

Exposure: Quantity of radiation intensity – ionization produced in the air by X-ray or gamma radiation.
- –Measured as “R” or “Coulomb” – C/kg an SI (Système Internationale [SI]) unit.

Radiation absorbed dose: The energy actually absorbed by a sample or a biologic system (depends on the matter).
- –Measured as “rad” or “Gray” “Gy” (100 rad = 1 Gy) an SI unit.

Radiation equivalent man: Describes the biologic effects of radiation. It is affected by differences in the type of radiation or irradiation conditions.
- –Measured as “rem” or “Sievert” “Sv” (100 rem = 1000 mSy) an SI unit.

For all practical purposes, 1 R = 1 rad = 1 rem.
Millisievert (mSv): Used to measure the amount of radiation exposure and the unit measured by the dosimeters.

A yearly dose of 620 rems from all radiation sources combined has not been shown to cause any harm to humans as per United States Nuclear Regulatory Commission (USNRC) [6] (Table 13.1).

Table 13.1 Cellular sensitivity to radiation.

Relatively more radiosensitive (rapidly dividing cells)	Relatively more radioresistant (slowly dividing cells)
Bone marrow cells	Heart cells
Stem cells	Large arteries large veins
Lymphocytes	Neuronal cells
İmmune response cells	Muscle cells
İntestinal mucosal cells	Mature blood cells
Breast tissue cells	Bone cells
Sebaceous glands of the skin
Gonadal cells
Thyroid cells
Fetal cells

Below is the known amount of radiation to various tissues that can cause some of the known effects:

Skin: This primary barrier to exposure, receives the highest dose. Depending on the dose, it may vary from mild erythema to denudation of skin. It may appear within hours of a dose of 6 Gy or more. Larger doses cause blistering, ulceration, and loss of hair follicles. Months later it may result in abnormal pigmentation.
Bone: Three different types of non-cancerous bone pathology may occur: osteoradionecrosis, spontaneous fractures and abnormalities of bone growth [8]. The threshold dose for femoral head necrosis and rib fractures is approximately 50 Gy.
Bone marrow: These are some of the most radiosensitive cells mainly due to their rapid division. A large dose may cause cellular death and depletion of blood cells. A dose below 05–1 Sv may cause only mild depletion of blood cells but a dose of 8 Sv or higher may cause fatal bone marrow depression. The maximum effect on the bone marrow is evident on day 9 post-radiation [9]. Ionizing radiation damages hematopoietic stem cells in a dose-dependant manner and the circulating hematopoietic cells decline due to reduced bone marrow production. In addition to damaging DNA, it alters gene expression and transcription and interferes with intracellular and intercellular signalling pathways [10].
Gastrointestinal (GI) tract: Effects of ionizing radiation on the GI tract is well studied and established. An article published in 1958 outlined these effects on experimental animals [11]. The stomach seems to be less sensitive than the intestinal cells. GI motility may also be affected. Bone marrow transplant, plasma transfusion and antibiotics may improve survival.
Intraocular lenses: The eyelids provide sufficient protection to the lens, however, a physician performing a procedure needs the eyes open and thus the lens is exposed to the same levels as the rest of the skin. The lens is also a protective shield against UV radiation damage to the retinal cells. Implanted lenses for cataract treatments are known to protect the retina. Even at supraclinical doses, the UV-absorbing capacity of chromophore-bearing PMMA and silicone intraocular lenses (IOLs) remains unimpaired [12

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